Overclocking the HD4870 in CF

Due to some cpu/motherboard problems i haven't had too much time to test these suckers properly. Unfortunately after forking out for a shiny new E8600, i've hit a wall at 4.75ghz where it is 100% prime stable at 1.4v but it won't even load windows at 4.8ghz regardless of voltage. I'm currently pointing the finger at my new DFI X48-T3RS for that little problem, but from what i've read these boards have no problem going over 475fsb. Not real happy so the results are limited to the old testing i did on my Gigabyte X48-DS4.

Test pad:
E8400 @ 4ghz (or maybe 3ghz?)
Gigabyte X48-DS4
Corsair Dominators @ 1066mhz 5-5-5-12
2 x HD4870 volt modded and watercooled
74gb Raptor
Corsair HX-1000
Everyday, bogged down Vista Ultimate 64bit install


Now it's time to play. Here's a shot of the cards in action. I know, it's a beautiful site and probably needs a NSFW warning :lol:.


The first 4870 i tested maxed out at 950mhz at ~1.4v on water. I had never tested the second 4870 so i wasn't sure what to expect when overclocking them in crossfire so i was hoping to match these clocks.

Testing was done using 3Dmark Vantage. I know there's plenty of people out there who don't like Vantage but FFS, i paid $$$ for this so i'm going to milk it until it dies!

I bumped the volts straight up to 1.4v and tested at 900mhz... pass! Huzah! That's respectful enough, but i wanted more. I then raised the clock speed up to 930mhz... again, pass! Still no artifacts or any signs of instability. Things were starting to look good for 950mhz, so i did just that. Set the clocks to 950mhz and ran Vantage. *crash* Oh well, she didn't quite make it. I managed to pass at 941mhz artifact free which is still a pretty extreme clock. Unforunately, much like when in single configuration, anything over 1.4v didn't help. I'd love to get some DICE on to these things but i can't forsee any money coming my way that i can justify to use on two copper pots.

Here's a screenie


Disregard the poor score, it's not exactly a tweaked os installation atm.

I've also since flashed these cards to the Diamond XOC bios which allows overclocking in CCC up to 990/1200. This should be plenty of headroom for all you extreme overclockers. Stock speeds are 800/1100 but i've edited them to 820/1000 for 24/7 use. I might post a quick guide later to flashing your bios, but there's plenty of resources out there for this.