With that setup it will not be the CPU that limits your OC but the motherboard/chipset, all of them should be able to run somewhere between 3.5-4.0 GHz (depending on silicon lottery ofc)
You won't be able to go much beyond maybe 360 FSB with the best of luck on G31. Around 330-340 should work, assuming you can set the FSB. That is also where your 667 RAM will run at 1:1 ratio, and the Intel chipsets won't allow anything lower anyway.
Try starting with the one with the highest multipler, in that case the E5400 or E6800
On these, don't go over 1.45-1.5v if you want it to stay alive. (65nm chips (like the Q6600) some do 4 GHz, but expect more in the range of 3.2-3.6 with moderate voltage)
E2140 (could oc to maybe 3.0, which means FSB around 330-340)
E2180 (same as above, doesn't clock much higher, but should reach it with around 320 FSB)
On these not over 1.35-1.4v (45nm chip (like the E8400 or Q9550) They can do 4.0-4.2 GHz, but 3.6-3.9 should be archivable with moderate voltage)
E5400 (high multi of 13.5 plus low FSB of 200 means it should go quite a bit before the board limits)
E6300
E6800 (12.5 multi means 3.5-3.7 is possible with 280-300 FSB, but also already quite high clocking lowering the multi to something like 9-10 would put you around 3.0-3.5 with 340-350 FSB)
E7400
E7500
or you could simply do a BSEL mod to trick the board into thinking the chip is a faster one. (tutorials are out there, but you basically put tape over certain pins) It takes most of the fun out of ocing the platform, but is easy to do even on boards that don't offer all the settings for manual oc. That would mean:
E2140 (200x8 = 1.6) ->(266x8 =2.12) -> (333x8 = 2.66)
E2180 (200x10 = 2.0) -> (266x10 = 2.66) -> (333x10 = 3.33)
E5400 (200x13.5 =2.7) -> (266x13.5 =3.59) -> (333x13.5 = 4.49)
E6300 (266x10.5 =2.8) -> (333x10.5 = 3.5)
E6800 (266x12.5 =3.33) -> (333x12.5 =4.16) here manual OC is needed.
E7400 (266x10.5 =2.8) ->(333x10.5 =3.5)
E7500 (266x11 =2.93) -> (333x11 = 3.66)
stock speed - should work fine - possible, depends on how well your setup does - with lots of luck/on a better board - won't work without better board & cooling