Monparacer, I'm in the same boat, I have the IP35-E as well so the Motherboard or Chipset FSB issue may not be the limiting path. Personally I'd say E2140 is a better value, which is what I just ordered. This is because it's not a matter of $50 difference, it's nearly twice the price when you compare $60 vs $109. With $6 shipping included, in effect you're paying about 75% more for E4500 when you're most definitely not going to get that much in performance. You'll likely see about 10-15% gain depending on application and overclocking probability. The only sure thing E4500 will get you is 2MB cache and its 11x multiplier. With that, you'll have a better chance at a higher probability for better overclocking due to 11x FSB. The 8x E2140 will probably top out around 3.2Ghz, and 11x E4500 may get you 3.4Ghz, which isn't that much of a difference once you're over 3Ghz. I figure I'll chance it and see if I get lucky on a good E2140. I hope it's a M0 stepping, but even that doesn't guarantee a good overclock.
Either way, 45nm Penryn is here and will definitely become mainstream in 2008. Also the E4xxx series is already known to be replaced by E5xxx series so the prices will definitely dive. On the other hand, as cheap as E2140 is, there's almost no room for it to drop much lower. May be $50 is about as low as a new dual core can go. I bet I can sell my E2140 next year for at least 80% of what I pay today. You can't say that about any of the E4 or E6 purchase. This is of course if you want to obtain max value for the purchase, which is what I strive to do. But that's just me. If you can use the additional cache (important in games if you don't have a powerful GPU) and want a better chance at higher overclocking, then by all means go for the E4500.