Arguably, I'll take 3.5 rules w/ PSCS 3.5, 2nd ed. fluff, 3.5 supplements, non-PS books on the planes (Some, like Beyond Countless Doorways are good for planar adventuring, because they detail oddball planes that wouldn't normally make it into WotC's stuff.) and setting material from just about anywhere, to fit the entire theme of PSCS's 'linking all the campaign settings together' vibe. I'll nix what's overpowered, but other than that...
I'll let almost anything in, if I can be reasonably sure that it won't break the game.