4x1GB makes it more finicky because of the northbridge has to work harder to keep things all 4 modules in sync in the dual channel. It all depends on your board spec. Typically P35 has native support up to 1333, which means 667mhz ram speed. You should be fine with that, but raising it above it may cause issue. I have 2x2GB with my P35, with only 2 sticks it reduces stress on northbridge, but the higher density ram also limits performance, and forcing memory to run at 2T. I can hit 400mhz just fine, but that's a combination of my DDR2-800 memory and IP35E board.
Bottomline is that more than 2x1 ram will result in slight performance hit, whether you go 4x1 or 2x2, but it's not much of a hit so I wouldn't worry about it.