From a gaming aspect are these cards comparable in core/memory? Or is the
3400 more for graphics?
FX3400 is a Quadro, not meant for gaming and way overpriced
for that use.
Compare a X800XL to a 6600GT or 6800GS for best values per
$.
There's not so much benefit in trying to compare core/memory
except when two cards use exact same core/memory, better to
just find corresponding benchmarks over a variety of games.
Then there's drivers.. personally I'd take a performance hit
from a little slower nVidia card just to get better drivers.