30 vs 60 is definitely noticeable, and anyone who thinks otherwise has either never seen 60 fps before or is lying.

Wait until you see 144FPS on a good monitor

I actually recently got a 144 hz monitor recently, though I think the difference is much smaller than 30 vs 60. Though it is (barely) noticeable.

40, 60, 100, and 200 were always the breakpoints I can see even on a 60hz monitor :) Though I did used to play UT1999 in a competitive environment