Prescott? Ouch. Your whole new system may eat less power than just that old chip alone.
Which would I get personally? e5200+G43. Faster than 4850e at stock speeds & overclocks much higher (even if that's not an object for you, it might be nice at some point in the future). Plus with the G43 motherboard you've got the upgrade path to one of the low power quads (65W, Q9400s or Q9550s) if you need it in a year or two.