considering there isn't really a single game out that you can distinguish the difference in speed between a 2.4Ghz and a 4Ghz now, i don't see how the extra 500Mhz is likely to help tbh. quad core is still the way to go. well tbh, if you're an overclock and constant, or even semi constant upgrader theres little reason to spend more than £50 on a chip, overclock it, then change your chip every 4 months. if you won't upgrade for ages, like 18months + then a quad core would be the better option.
also would think a 3.16Ghz dual core won't be the cheapest option for a chip? not sure what the range of dual core 45nm cpu's they are planning to release but assuming 2Ghz to max 3.33Ghz(poss 3.5Ghz) this will be between the 1st and 3rd fastest dual core, meaning probably as expensive, or more expensive than a quad core at 2.4Ghz. for benching, encoding, 3d work, 3dmark, anything the quad core would beat a 4.7Ghz dual core easily, and for gaming, they'd both be the same even at stock. a q6600 is easy to hit 3.6Ghz with water, i'v hit 4Ghz, 4Ghz air should be possible on at least some of the cheapest quad core penryn's, can't see a E8500 being useful anywhere really.