You might want to turn to Google for FCPX vs Premiere comparisons
The nutshell version of it is Apple totally revamped FCPX to cater to the amateur Uncle Bob crowd, lowering the price and leaving out a lot of pro-level features and alienating droves of professionals who've jumped ship to either Premiere or Avid.
There is nothing missing from FCPX that anyone with a budget of under $20k would miss. Most of the features of FC7 are there, they have just either been tweaked, moved, or vastly improved. The multi cam, audio sync, and little interface tweaks make me wonder how I ever survived in 7.
I can't speak to the differences between FCPX and Premiere, as the last time I used Premiere was 8 years ago. Rather than focus on the differences, maybe the question is, can I get professional results from FCPX/Premiere? I would say yes to both. It's kind of like the differences between Nikon and Canon