Okay, immediately on pressing the power button to start the computer with the GTS 450 installed, I got 3 or 4 beeps and a prerecorded message, "System failure VGA patch" with a black screen and never even got to BIOS.
I tried it a few more times, and double-checked everything, and still no soap.
I do need to mention, my monitor uses an older three row plug, an analogue 15-pin D-Sub VGA, whereas the GTS vid card only has two DVI ports, but I used a certified video adapter to match it up to the GTS video card port, so I am not sure if that jinxed it.
It's too bad, as the GTS has 1GB of ram vs. 256MB for my 6800 GS.
I know where to get my hands on an nVidia 6800 GT, so I searched for a comparison, and the GS and GT are already very close to each other in performance as shown here which gives a thorough comparison;http://www.trustedre...00-gs-reference-card
Here are more comparisons between the 6800 GS vs. GT, and they are quite close;http://www.bit-tech..../07/nvidia_6800_gs/1
At this forum...http://www.bit-tech....a_6800_gs/comments/2
...user Tim_S says he tried to run a 6800 GS paired with a 6800 GT in SLI mode, and 'tried several driver revisions with no luck'.
So the 6800 GS is back in place and everything is working fine again.