I just completed by Coffeelake build and had trouble installing windows 7 on it, so I used win 10 in the mean time while I figured out how to get win 7 updated and working. Something I noticed immediately with win 10 is just how slow and sluggish it feels compared to win 7 in all but the most basic apps. Win 10 is faster when I have like 3-5 apps or youtube tabs open at the same time, but win 7 handles extreme loads much much better. I can have like a dozen youtube tabs open and be playing a game at the same time on windows 7 without noticing any lag, while on windows 10 it becomes extremely noticeable. I dont know if it's just me or what, but task manager and fraps report the same or a little bit better performance on windows 10. I have a second monitor which I leave task manager open on and glance every so often to compare.
Both OS's have their own identical SSDs(160gb Intel 320), they are running on the same PC.