Wow !! very detailed testing there harvik, good job !!
I am saying, keep a very high CFM 120mm fan next to the SLI bridge over the 2 cards, parellel to the board, will give you slight headroom for better clocks IMHO.
Also IF possible check if the thermal paste on the core is making good contact with the heatsink, most of the times i have found, it doesnt do it.AS5 will help you cool the card a bit.
I guess you are using the P5N-E SLI mobo for testing, its based on the 650i SLI chipset so you can run the RAM in unlinked mode which takes memory out of the OC equation and can push the CPU even more.
BTW, i hope you are cooling the PWN area with 80/120mm fan right ? If not, do that, keeping the PWM cool, helps in improving stability.