Actually it's exactly the other way around. X38 sucks for 45nm quads. P35 not.
Enough results here in the forum for proof too.
My CPU makes 3.8ghz on a 70 bucks gigabyte DS3 P35. Can't even get 3.6ghz stable with more voltage on the x38.
Hand picked x48 might yield better results but not better then on a P35.

If you look for through this forum for good 45nm quad overclocks you will find out that most achived thm on a P35 board.