Mine stable with 3.8ghz @ 1.31ghz  
But to be stable for 4ghz(400 x 10), I have to bump up to 1.41v  Thats a full 0.1v just to increase a mere 0.2ghz..so no point really.
I haven't given up though by lowering the FSB to 380, and multi to 10.5, but manage to stabilize it to 1.38v only.

IMO, anything above 1.3625v seems unnecessary for 24/7 (on 45nm) and desperate if you want to show off to you peers  ,  but for benching, once I briefly pump the E7400 to 1.45v, thats unrecommended, but like I said, for benching only.
I hit 4.2ghz that time but I never posted it on LYN because I never documented it (screenshots, prime95, etc.)  for proof/evidence, and don't want to bench it that far ever again because it WAS a scary experience.. (constantly in my mind thinking if the proc ever gonna die on me... )
Anyways bro, I believe you can get much lower vcore for 3.8ghz, keep us updated with your progress 
Since this it like a lottery, I will place a bet on 1.34v 

i got my e7200 running at 3.6ghz

vcore=1.28v
multi= 9 x 400
ram= kingston value ram at 800mhz 5-5-5-15
vdimm= 1.8v
FSB:DRAM= 1:1

idle temp= 36c
load= about 55c

3.6GHz in what FSB & multiplier?
What your ram speed & timing?

-pWs-

Can buy those RAM sink, (range from RM9 - RM25) they do a pretty good job though.
Buy yeah, I didn't realize the guy using the good ol' KVR. 
Probably without the heatsink 900mhz is alright, but need to get up to 1000mhz for best PL setting for C2D and Dual core CPU's.
FYI, there's a manufacture,(I forgot its name) produced a perfectly 1000mhz DDR2 ram (yes, not 1066mhz) to cater to the optimum 2 cores proc for PL tweaking.
There's something special about the combo of 400FSB + 5:4 + 1000mhz RAM to achieve low PL value...for 2 core procs especially.

@plush, I re-opened one of my closed thread which might enlighten you with this PL thingy, as well as RAM timing tightening, tRD, etc.

http://forum.lowyat.net/index.php?act=ST&f=5&t=1255768&st=0

This article, if you read it and study it carefully, you be in a totally new level of OC'ing:
http://www.anandtech.com/mb/showdoc.aspx?i=3208&p=1

OC'ing the CPU is just the first step like I mentioned, the final step is the whole system tweaking.