If real-world is anything like the graphs, it will be pretty good upgrade.
I've been doing a few more informal tests (haven't had time to do a 1-2 day burn-in), and I've seen most CPU-intense operations are 3-5% faster (some more so) on the 64-bit release.
There's the noticeable performance benefit that you can actually use the 8GB of RAM on the new model.
There is an 8GB model? I thought the largest was 4GB (which I have)?