now running fax with sli turn, my question would it be best to my computer with sli turn off

Yes, turn SLI off. Back in 2005-2006 when FSX was designed, SLI didn't exist (as far as I can remember), so the game was not designed for SLI, and cannot use it. It will actually hurt performance a tiny bit, because the extra graphics card eats up a little bit of CPU load.

100% correct. The only reason you'd want sli in FSX is for nvidia surround so you could span the vc across 3 monitors. If you're not doing that then its best to avoid sli (for fsx).

Yes, turn SLI off. Back in 2005-2006 when FSX was designed, SLI didn't exist (as far as I can remember), so the game was not designed for SLI, and cannot use it. It will actually hurt performance a tiny bit, because the extra graphics card eats up a little bit of CPU load.

SLI existed in 2005 - it was originally a technology developed by 3dfx, the first 3D video card maker back in the late 90s/early 2000s. Nvidia bought them when they went under and implemented the technology in their cards.The reason it's not effective in FSX is because FSX is not GPU-limited. SLI is effective in games that primarily use the GPU, not the CPU like FSX does.