David,
Although I sometimes get warnings that my iMac is not up to task, the linmited 4K tests I've done, worked well.
I loved working in legacy FCP versions; a very comfortable and dependable "user relationship". But increasingly, I've used X as the go-to NLE and while there are many things that Legacy can do that I wish X could do, I don't miss all the rendering, the clunky titler, and more. The past week I had an unexpected project drop with an incredibly tight turnaround requirement. I was able to work with mixed footage, including hundreds of un-resized stills – effects, CC within the app, etc– export it in several formats from an unrendered timeline…and it all came together very, very fast. Never would have happened with FCP7 and earlier.
One last thought: you may find that it's not your cup of tea. but I'm guessing you'll find getting acquainted with the app interesting and enjoyable. There are so many really good instruction videos on this app it's hard to make a recommendation. But try watching some of them; IMO, they really make a big difference in whether a potential user has a fun experience or not.
Russ