On my 280 with the standard cooler I can bench it upto 730 / 1566 / 1350. If I push core above 730, 1566 shader sends it artifacting like crazy. To use any higher you need to volt mod it. There is very little to gain besides the extra heat dump. The most you can push if you have a gem of a card is 1620mhz shader and 760 or so core. Memory is very dependent on how good your cards IC's are. Early 280s have very high binned Hynix ICs are easily push 1330-1375mhz memory. Later ones might not be so tolerant of high frequencies since Hynix introduced a 1300mhz bin a month or so after the 280 was released. If you want to use higher shader which gives better Vantage results, lower the core down to around 730-740.

Just for reference in Vantage my best at 730/1566/1350 is 15913 on 180.84, so you should be able to push somewhere around there. I run it normally at 670/1458/1300 flashed in bios, so 1300mhz memory shouldnt be too much of a problem.

Hope this helps!

I've modified an XFX bios version 62.00.1C.00.86 which is probably the latest or one of, which uses slightly looser memory timings on timing set 0/2 to accomodate for the higher memory frequency I push (setup according to Hynix GDDR3 datasheet for N3C bin (1300MHz 0.77ns). If you are interested, just shoot me a message and I'll be happy to send it your way.

I'm very tempted to go the watercooling way soon as I grab a 2nd 280 for SLI in a couple of months!

Your setup looks shmick