I7 Build CM 690 GTX260 SLI Heat Problem

Hello to all:

My Build:

i7 920
2 GTX260's in SLI
Cooler Master CM 690 Nvidia Edition (With all 7 case fan slots filled with stock & Best Buy quality 6x120mm and 1x80mmx15mm)
6 GB Corsair XMS3 DDR3
Corsair TX850 PSU
Asus P6T MOBO
Vista 64
Noctua 1366SE CPU Heatsink

My Problem:

With GPU (and all other fans) at 100%, after about 15 minutes of Furmark stability test GPU's hit 90c or so and crashes system. It also happens when gaming for about 45 minutes.

My Question:

How can I lower my GPU temps?

I'm looking for suggestions from other people who have had success lowering their GPU temps. I know I'm having an airflow path problem due to the massive graphic cards and extra cables from the PSU. The intake fans are at the bottom, front, and sides of the case. The exhaust is the 2 120mm on top and the 120 in the rear. Would swapping all the fans out with higher CFM fans work to overcome the 10.5" graphic cards and extra PSU cables that are blocking the airflow?

I'm open to cutting some holes in my case to add a fan or 2 (the system is loud as h*** already), but the perfect place to mount the fan would require me to cut into the plexiglass or plastic or whatever it's made out of window on the side on the case.

FYI I had CPU heat problems as well. The Noctua CPU cooler cured them by dropping the 100% load temps from 100c to 60c (3.8 Ghz OC) in the Prime95 Torture Test.

Thank you in advance for your replies.