oops...
Just too late 
I just tried upgrading to CC35, but also that didn't went very well...
Contrary to what the person on the chat told me, 2 of my 4HDs do NOT support the CC35 firmware...
So now I have 2 CC34 HDs and 2 CC35 HDs
This is definitely not what I wanted and I hope this doesn't impact the ability to run a stable RAID5 on them
not sure if it helps, but here are all *.ata files I have now (you can read what firmware is on inside the file):
http://users.telenet.be/Mastakilla/HDs/ata.zip
I just talked with someone from the US chat support and he didn't really understand why I was told that CC35 should be for all my HDs either and suggested me to contact EU support about it again (region differences )
He did have an actual look at this thread and gave some valuable input:
"David K.: There is a question you had in the first post though that I can answer: Firmware updates are typically specific fixes, rather than performance updates so it's not always recommended to get the "latest and greatest" version of the firmware. You mention " is this new firmware "not advised" for ALL Barracuda LP HDs (perhaps it is only advised in very specific situations?)?" Firmware is more designed for these specific situations. "
He also told me to test if the CC35 HDs still have the clicking issue and then contact EU support again... (that's what I'll do now)
You keep on amazing me fzabkar 
I had a look at the PDF and I'm wondering when this SECURITY ERASE UNIT is triggered.
If the SECURITY ERASE UNIT times is the ONLY "real difference" and it is triggered only when "emptying" the HD in specific way, then I guess the firmware won't make any difference in day to day use.
Also for the RAID controller it wont make any difference. (I was afraid the firmware might also change things like power saving settings)
About forcibly updating the firmware, I understand that this is only advised if I'm really sure it is compatible and necessary (else it may brick my drive)
So unless Seagate support can convince me to do this, I will not do it...
I'm not sure what I'm doing wrong, but I"m having a really hard time getting a decent answer from the EU chat support (in contrary to the helpful US chat support person, who was restricted from helping me with the firmware related questions because of region differences)
...
Maarten Van der Auwera: anyway... can you please check the difference between CC34 and CC35? I would like to know if there are any changes in the power saving settings (which could greatly impact the ability to run in RAID)
Ali B: The CC34 has a seek time of 14 ms and hardly any difference
Ali B: CC34 firmware -> seek 14.5 ms
CC35 firmware -> seek 13.5 ms
Ali B: Is there anything else I can help you with ?
Maarten Van der Auwera: ok thanks, so the difference is purely a performance difference?
Ali B: Seek time only
Maarten Van der Auwera: ic... do you have an idea why CC35 isn't compatible with the 9XW HDs then?
Ali B: No sir
Maarten Van der Auwera: Cause I've read tricks to force the CC35 on 9XW drives, but I really don't want to do that unless I'm sure it won't do any damage
Maarten Van der Auwera: can you perhaps forward that question to a technician?
Ali B: I am not sure sir that`s why I suggested to contact the company they are going to set up your raid
Maarten Van der Auwera: I am "the company" that will set up the RAID
Maarten Van der Auwera: it's for home use
Maarten Van der Auwera: but again, this is not related to RAID
Maarten Van der Auwera: I just would like to know the difference between the 9XW and 6XW drives
Maarten Van der Auwera: and CC35 isn't compatible with the 9XW drives
Maarten Van der Auwera: Maarten Van der Auwera: and CC35 isn't compatible with the 9XW drives --> I mean "and why CC35 isn't compatible with the 9XW drives"
Ali B: there is no difference between the drive there are same models a Brarracuda LP SATA 3Gb/s 2TB
Maarten Van der Auwera: that sounds very weird, no?
Ali B: no sir
Maarten Van der Auwera: why would there then be a firmware check...?
Maarten Van der Auwera: then CC35 should just work eh...?
Ali B: I have already checked the drives do not require no firmware
Maarten Van der Auwera: but earlier you said the CC34 to CC35 firmware gives better seek performance
Ali B: I did not say that , you asked me what is the difference and I said there is no difference if you look above my answer
Maarten Van der Auwera: so it may not be required, but it does seem something people may want
Maarten Van der Auwera: Ali B: The CC34 has a seek time of 14 ms and hardly any difference
Ali B: CC34 firmware -> seek 14.5 ms
CC35 firmware -> seek 13.5 ms
Ali B: hardly any difference
Ali B: anything else I can help you with ?
Maarten Van der Auwera: I guess not then...
I'm not sure if what he sais is true (I'll check the seek time later this evening), but he claims the difference is purely in seek time
In meanwhile I tested the CC35 HDs again and, as I feared / suspected, the EU tech support person lied to me again
There is no performance difference what so ever between the HD before (CC34) and after (CC35) in both random read and random write tests of HD Tune
Also the sequential performance is the same (less than 0,5MB/sec difference)
I have repeated the tests multiple times
Now this is the 2nd time that the Seagate technical support chat of EU lied to me... First they confirm 4 times that all my 4 HDs are candidates for the CC35 (only 2 of them were) and now they lie about what the difference is between CC34 and CC35... (it clearly isn't access time or "no difference at all")
Now I know 1st level support is only for solving the easy problems and for getting rid of as much difficult questions as possible, but that doesn't mean they have to lie to me twice in a row... I think I did enough research before contacting them to deserve at least 2nd level support
I'll now try to put this all in a nice email and hope a more honest person receives it, cause I just lost all trust in the Seagate EU chat support
