GTX 460 O/C question

[SHaFT7]

I've got this:

http://www.newegg.com/Product/Product.aspx?Item=N82E16814125333&Tpk=gv-n460oc-1gi

currently i'm O/C'ing to 845 core / 2000 mem on stock voltage. as long as i keep the temp around 66C or so, it works fine. Today it has been warmer, and we've had the windows open, so I've had to drop the O/C down to 800 core / 1800 mem to keep it stable, or BFBC2 crashes once it surpasses 70C.

Do I need to up the voltage at all to keep it more stable at 845MHz? or is 70deg the max of what these cards can handle?

I DO have a custom fan profile that ramps up to 100% fan by 65C.

 

[SHaFT7]

update: stock voltage for this card was 0.937v. From my searching on the 'net, this seems low compared to a lot of other cards. I did a test of putting it at 0.975v and am 6 min into furmark running at about 82C (ambient is about 82-83F (windows open, A/C off). maybe the voltage was the ticket....