the e6300 sits between the 4600+ and 5000+, the e6400 sits between the 5000+ and FX62
considering you can only get the oem e6300, you will be paying roughly the same as you would for a 4600+ when you include a decent motherboard for both
if youre happy having a product with no guarantee (scan dont mention it but thats how it seems to be at intels end) the e6300 is more for your pound... for the retail version they become more expensive and the 4600+ is a bargain for an unnoticable drop in performance
if you overclock the e6300 is by far the best though
and both have great upgrade prospects, you can replace AM2 chips with AM3 when they arrive, and obviously core2 has just started so there should be more of those coming