I very much doubt they will issue a replacement after having one logic board replacement, Apple will request another chance to fix the problem first.
I had a similar opinion in that I did not want another 8600GT after having 2 fail already (the original and the replacement), but I was assured this was very unusual and that for anything else to happen, I'd have to go through another repair cycle first. Had my computer come back without the other damage I mentioned, perhaps everything would have been OK, but I highly doubt it with both the original and a rev2 not correcting the problem.
If you do speak to Apple, make sure you go through to customer relations, they seem to be the highest level a customer can go to without having to write to Apple corporate offices.