So i got a new 5K iMac, base config except SSD instead of Fusion drive. Display is beautiful. Video runs smoothly. Processing (Lightroom) is fast. However the finder is super slow and laggy. Opening up new finder windows, previewing picture files, moving files, scrolling in file lists: all this has lags of several seconds, or up to almost a minute. Sometimes even the cursor is slow. HD is about 25% full, I have hardly used it on the web (IE little chance of virus). I mosly use it in Lightroom and PS to edit photos, and finder to shuffle and organise JPG, MOV files, etc. I have shut off transparency, spotlight, and otherwise followed all other available advice to speed up the machine. It still feels like a 1994 macintosh with full hard drive instead of a 2014 imac with a brand new ssd. I have to force quit finder several times per session. In fact the issues are so annoying that i have had to move my files to an external and using my 2008 imac to shuffle files, renaming, preview videos etc. I suspected this could be a Yosemite issue, but after installing that on a 2011 Air, I see no issues with that computer. So how come this iMac is able to spit out raw conversions faster than ever before, and play video smooth as silk, but still need several seconds to draw out a single finder window? Yosemite bug or hardware issue? Any input appreciated as I am quite distraught here.