GS vs GT???

I'm looking at a new GFX card for the new system that I will hopefully be building soon.

I wanted to get something that excels in games but not too expensive. (Can't afford an 8800 unfortunately).

I was looking at the 7900 GS as per THG's newest Video Card article. There are a couple of nice XFX 7900 GS cards on Newegg that caught my eye.
One has a 600MHz core and 1600MHz memory for $170 after rebate, and the other has a 525MHz core and 1550MHz memory for $145 after rebate.

I also found a Foxconn 7950 GT with 550MHz core and 1400MHz memory clock, at $190 after rebate, and has 24 pipelines as opposed to the GS's 20 pipelines.

My question is, do the extra 4 pipelines make a big difference? The first GS I listed has higher core and memory clock speeds, so would that offset having 4 less pipelines? Granted, the difference in core clocks is only 50MHz, but the 200MHz difference in memory clock speeds is a lot bigger, and as I understand it, memory speeds are becoming more and more important with these newer cards.

If anyone could clarify a bit on this, I'd greatly appreciate it.

One last question, and this may be a really stupid question so bear with me: Is there any difference in getting an nForce MoBo and using it with an nVidia card or an ATI card?

Thanks

Agreed.