Yeah, but – every other NLE has no issue whatsoever to play a single stream of, say, 720/25p ProRes from a measly USB2 drive. And simple cuts editing is fast.
FCPX has BIG issues working with larger projects, even from eSATA G-Tech RAID 0 with speeds over 130 MBps on a 8-core Mac Pro. Opening a keyword (bin) almost always slowly re-reads thumbnails, with RAID thrashing. When I switch to another bin and back, it SLOWLY rereads thumbs again. And most of my 22 GB RAM sits there unused. FCPX should be WAY more aggressive with RAM.