I am looking into building an entire new machine, new graphics card and all, however, I was just curious if there can be any use for my current GeForce 6800gs (PCIe)? I've seen that a lot of the new motherboards come with both PCIe 2.0 and PCIe 1.0 slots, so, I was just wondering if I could get any use out of my old card?
Also, since I am building a whole new machine, just wanted some input on if it's worth it to do SLI/Crossfire with mid-lower end cards or just buy a reasonably high end card? And I know that SLI/Crossfire varies with performance on how they are used (which games/programs/etc.), but just speaking generally long term, what's the better option? I am leaning towards just a single higher end card (something like the a GTX 280), that way I can save a little on the motherboard and not have to worry about buying on with two PCIe 2.0 slots.
Depends on what resolution you use, but overall yes.
Here you have some charts comparing a lots of cards(right now every new card obliterates your 6800gs)
Knowing your budget would be nice, but since you wanted a gtx280, witch would be around 250-300&+, you could go for a HD 5770/ HD 5850. The HD 5770 is around 150-200$ depends from where you buy, the HD 5850 around 230-300$. Comparing to a gtx 285 that cost from what I'm seeing at newegg 320$... look at the charts ^^
Later on you could crossfire the ati you choose(since they cost less and perform better than the 200 nvidia series)
So, definitely yes, they will hold you for a few years, more if you crossfire them and since they are cheap....
Then look for the HD 5850, and see if you can find one with low price and go for it, as it kills the nvidia 200series of 300$
The HD 5770 is very close in performance over the gtx 285, with a price on 150-200$, so it is a very very good deal. With that card you will save money. If you want to spend a little more then go for the HD 5850 witch kills the gtx 285, and is cheaper ^^.
Now make up your mind and you are set. Even with 1 or another, you will see a lot of improvement over your old card.
Edit, along the way I forgot to say, that the new ati series HD5xxx has new tech(dx11,tesselation etc...) so they are better future proof than the nvidia 200 series. You could go for the new nvidia 400series too for future proof as they also have dx11 etc... but they are expensive and perform evenly.