well, that may depend on whether you have already bought Melodyne Essential (Pro will come with a license to it, that's £90 if purchased separately). Artist Booster Pack is a great value, also Artist is less expensive to upgrade in future.
look at comparison and see what features from Pro you may need. I personally have Pro, a list of things I will miss with Artist:
- import song data
- multiband compression/expander
- acoustic drum kits and loops
if you think that you will notice 32-bit vs 64-bit difference, likely you won't, for most applications either is good.
