if im not mistaken..default gpu clock for 9800gt is 600MHz..taken from wikipedia..so i guess there is no problem with that but u may lose the power save..btw..im using gigabyte 9800gt oced version..gpu clock is 740MHz by default..

oh..almost forget..u can use prime95 to stress test the gpu..

prime is for cpu.

u can use ati tool  or furmark or just plain old 3dmark and loop it.

gpu is more important??u mean gpu clock..errrrr..i think yes..if the gpu is same batch(9800gt not same as 9800gtx)..need to take consideration bout how many cores in one gpu chip..

heh..i nvr tried prime95..lol
anyway..i once downloaded nvidia ntune and the software got function called stability test..nvr tried yet..  

izzit the score is an average score?..need to do is several times to get a consistant result..btw..in my opinion..to get the most performance from the gpu..or from any oc activity..we need to test many aspect apart from these three..mybe the voltage also need to be taken into consideration..

err..xjamin..i nvr tried bcoz afraid to fried my gpu..hoho

p/s:any sifu here?..i once read that we need to increase voltage if we oced the gpu clock over the limit when the instability occur..hurmm

wow..if i were you dont increase the PCIE voltage..depending on the mobo, the tweaking should be in bios..google ocing gpu/cpu if u still wanna..the 3dmark, u need to run several run per setting and get the most consistent mark to call'ta own..good luck..

before u flash use gpuz to back up ur bios , and find/learn how to flash back bios on Bios menu there...if not ur gc = rock  ,some card have dual bios then that one no need scare 

diadokmai, before you do any serious OC'ing, we haven't inquire one very important data that seems to be overlooked... the temperature. 

Tell us what's is your IDLE ~ LOAD temperature of default setting (non-OC)
then for sure tell us the  IDLE ~ LOAD temps when you OC the card.

You can  run Furmark OR use Speedfan which have the graph that logs your GPU temps (or download GPU-Z, which also has an option to logged in the GPU data)
THEN try 10 mins of the most graphic demanding game you have and see what maximum temperature does the GPU hit  (both in OC'ed and non-OC'ed that is...)
The difference running Furmark and gaming (for gathering data) is that Furmark is a synthetic 'stresser' and gaming is real-world testing, so Furmark you get you higher temps reading than normal gaming because Furmark loads your GPU 99.9%, and the average games will load your GPU around 80%-90%.

Anyways I use to owned an XFX 9800GT (600mhz/900 DDR3) exactly a year ago,
When OC'ed ( 700mhz / 1000 DDR3), I think the idle temps was 58c-60c and the load temps was max 75c using aftermarket (Zalman) Cooler.

Other comments:
>If you were happen to tweak the PCIE voltage in BIOS, I dont recommend going past '104' with the G92 (9800GT chipset), if you past 104-105, the risk comes in bro...
>Flashing the bios is easiest way, but also easy to screw up if you are uncertain of what you doing, usually from typo when inserting commands, etc.

just use rivatuner to oc,use atitool to scan artifact,use furmark to stress for stability.

after oc,use ati tool for 1-3 hours..no artifacts.if you still want to oc.just oc higher and scan for artifact..if ok d,use furmark for 3-6 hours..bear in mind.cooling is very important..happy ocing and dont oc one time 100 mhz.move little by little..