Hi!

I currently have a Golden sample (overclocked) 6800GT card with 256MB DDR3
ram. Now I wonder if I was to trade up to PCIe system, what would be the
cheapest card with at least the same or slightly better performance I could
get?

Best Wishes

I researched AGP + PCIe motherboards some time ago and I seem to remember
that there was a significant video performance compromise. Hopefully it's
no longer an issue, but you might want to check it out.

I did not get the impression you were looking for a crossover AGP/PCIe motherboard - I would advise against that, too many compromises.

I think what you are asking is not possible to answer. Too many variables. My advice is to budget for 2 Gb of RAM (assuming new PC will have Vista) and the best graphics you can afford.

Check out Tom's Hardware article, The Best Gaming Video Cards for the Money: February 2007.