Q1: Read this
http://www.tomshardware.com/2007/10/...el_processing/
Q2: There is nothing in the pipeline to replace PCI-E. Right now only the addition of more video cards in one's system is on the horizon. New cards are expexted in novembre/december fron NVIDIA.
Q3: I just went SLI. I used to run a single ATI X850XT card and must admit that I find SLI a pain. For iL2 I had a multitude of issues that I had to resolve before it ran good. My ATI card was A LOT easier to setup.
Now does that means you should discard NVIDIA SLI... I don't think so. When you get it working it is a very stable and capable platform. But so is ATI Crossfire setup. Right now NVIDIA as the absolute performance edge... but who knows in the future ??? I personnaly prefer the image quality of ATI but it is not like I find NVIDIA horrible... just that ATI seems better (well to me atleast).
IMHO it all boils down to how much you are willing to pay and what gives you the most bang for the buck. On this read this:
http://www.tomshardware.com/2007/10/...for_the_money/