Hard to say about the new Final Cut since it is not out yet. However, if the multithreading support is as good as it sounds like, then the i7 should be worth it.
Nobody has benchmarked the new imac with specific apps so you're not going to get those specific answers yet.
But there are tons of sandy bridge benchmarks out there going over various video and photo tasks and those will give you an idea of where these imacs are at for those types of tasks. Anandtech.com is my favorite review site.
Yeah editing those 18+ MP photos and 1080p files will be a bit speedier on the i7. Not night and day faster, but every second you save over its life can be beneficial.
Yeah editing those 18+ MP photos and 1080p files will be a bit speedier on the i7. Not night and day faster, but every second you save over its life can be beneficial.