Am using KVR533 Hynix C4 sticks and so far so good. I "burned in" using Orthos RAM test for a few days consecutively at 4-4-4-10 2.0V.

How much did you buy your sticks for ?

You guys have nice timings there... I tried to go for DDR 800 again just now, 5-5-5-12 @ 2.1V ---> Failed Orthos

So now I'm running at 370MHz @ 5-5-5-15 @ 2.1V ---> Orthos 8 hours no errors yet~! Maybe try to tighten or up the speed tomorrow...

You guys did burn in like this with your RAM? Or can it just clock at DDR800 straight out of the box? Since mine is 1GB modules... You think that make a difference?

--- Update: ----
I finished orthosing 370MHz @ 5-5-5-15 @ 2.1V for 13-14 hours without errros and shutdown my computer for the night. Restarted it this morning.

I'm Orthosing now at @ 400Mhz / 2.2V / 5-5-5-15 for 2 hours already without any problem yet... Hopefully there is no problem later~! If you read the first post I posted, I tried this setting when I first bought the RAM and it failed Orthos within 3-10mins... Now its working!

I wonder does this really show the 'Burn-In' effect in overclocking... 

I guess that's the case~!

I mentioned earlier that I was orthosing without problems at DDR800, but it failed just a momment after that... I pushed the voltage to 2.3V DDR800 @ 5-5-5-15, still fail memtest. Now I dropped back to 370MHz and use it for a few days more before trying out for DDR800 again...

Sigh, maybe Kingston sticks OC better than Hynix? Hahaha... Or I'm just unlucky with my pair of C4 , getting the 'binned' ones. Will give it a few more days before selling it and swap back to my OCZ...