The NOTE has the fastest and best dualcore processor.
...with that said there's barely any performance jump going with the S3 (despite having the best quadcore processor).

You can get the NOTE anytime you want.
The prices have stabilized, they wont be dropping that much/fast. Which means if you don't like the features/size you can sell it, get your money back and then buy an S3.

Things to consider:
-TouchWizz is the best OEM ROM out there (its closest to stock)
-There's perm root/unroot you can use on the 2.3.5 OEM ROM
-You can apply a CWM and save the original rom that came on the phone
-Flash anything you like (neobuddy's AOKP 1.4.26.1 or m3dd0g's Liquidsmooth v1 or pvillasuso MIUI RC1 or official CM9 beta)
-Revert to original for repair/warranty/selling