....However, your mention of converting your footage to ProRes is a different thing. ProRes will of course edit well in FCPX as that what it was designed to do. Despite current hardware/software being able to handle it, h264 is still a ****** editing codec. Any lossless format (I know ProRes isn't technically lossless) will edit well in the common NLEs.
Yes, generally correct. Transcoding to ProRes or other low-compression or intraframe codec will usually give more responsive performance on most editors. Historically Final Cut required transcoding to ProRes, whereas starting with CS5 Premiere's Mercury Playback engine was so fast it could edit high def H264 with good performance.
However this began to change with FCPX, and for approx. the last two years it has had roughly equal performance to Premiere when editing H264 up through 1080p. It is generally no longer necessary to transcode to ProRes in FCPX -- it is just like Premiere in that sense.
But due to that history FCPX retained a built-in transcoding and proxy feature. By contrast Premiere's Mercury Playback was so fast they did not need transcoding, so it never had this and does not today.
In fact it says on the Premiere overview video it
"allows editors to work with 4k and beyond, without time-consuming transcoding", and "never needing to render until your work is complete":
https://helpx.adobe.com/premiere-pr....html?set=premiere-pro--get-started--overview
Unfortunately Premiere CC performance degrades exponentially on H264 4K material, at least on a top-spec 2015 iMac and a 4Ghz Windows 10 PC I tested. In my back-to-back performance testing on a top-spec 2015 iMac 27, Premiere does not deliver responsive timeline performance on H264 4K material, whereas FCPX does. When fast forwarding through the timeline I would estimate the viewer update rate of FCPX is about 20x faster than Premiere, likewise lag on JKL input is much less.
If you transcode H264 4K to ProRes (about 8x the size), then Premiere is fast. That means manual transcoding using external utilities. An approx 1 hr two-camera 4K shoot using 100 megabit H264 is roughly 80GB; transcoded to ProRes that's about 640GB. The latest version of FCPX does not require this for adequate performance, but if desired it has built-in transcoding and proxy features so you never worry about moving files or getting them out of sync.
This is all relevant since it affects hardware choices, which is this thread's topic. If Parsuto will only be editing H264 1080P on Premiere CC then almost anything will work -- iMac, Mac Pro, Windows machine, etc. If he will be editing H264 4K, that is a lot harder for Premiere and he may need to transcode to ProRes (which means a lot more disk space) or get a really powerful machine.
If he wants to consider FCPX that is OK but generally I do not recommend changing editing programs you are familiar with. Despite these issues Premiere is a good product and the suite (Prelude, Audition, After Effects, AME, Photoshop, Illustrator, etc) is very rich and diverse.