it is a close match between Venice and orleans. the higher memory bandwith puts the orleans in front in some areas, but DDR1 has lower latencies (which is a bigger advantage on K8 CPU's), and the Venice has a lot fewer bugs, so it performs better in the majority of cases.
overall, the venice gets about 5% better in performance.
AM2 CPU's and motherboards are about the same price as socket 939 ones, but it will cost more to get DDR2 memory
so overall, I'd say it is not worth it to get AM2 yet, unless you plan on upgrading your CPU in future and don't want to get a new motherboard.
the memory controller on the orleans is basically built off the DDR1 memory controller on previous chips, so it's not really optimised for DDR2 yet.
one of the bugs with the memory controller is because of the odd numbers of DDR2 (533, 667). the problem is not the ability to reach the higher speeds, it's the multiplier and HTT speed used that just don't get those exact numbers.
I think that's why AMD decided to use DDR2-800 as standard. that number kinda agrees with the memory controller.
if socket AM2 will support DDR3 (which I think it will), then I think DDR2 is kind of a stopgap for AMD anyway.