Well, to be honest, I main Bard, probably one of the most ping-dependent classes in the game. Machinist would be in a similar boat, I'd think. People talk about Ninja lag, but I think Bard players had it a lot worse, many just don't realize it because most people ran for the hills as soon as WM became a thing and never tried to really optimize the class.
I'd pretty much notice immediately when I go through my opener and notice I still have like 2 seconds remaining at the end to fit in an extra GCD, and the delay between activating each buff is significantly shortened AND
Bloodletter doesn't really clip into things anymore. Not sure how it's like for other classes as while I've leveled virtually all of them, I haven't taken them into serious raid content.
Uh... I actually do have video footage of sorts to compare, I stream my roulettes sometimes for possible documentation purposes. Though since I don't have Twitch Prime, my pre-transfer footage is going to get nuked soon.
May 6 (Before Transfer):
https://www.twitch.tv/videos/140620010
May 17 (After Transfer):
https://www.twitch.tv/videos/144574932
(Before anyone asks, that's not my real raid opener, I can't be expected to use potions all the time. However, the standard roulette opener I use has actually made it really easy to see exactly how much of a difference going from 110 ms to 24 has made for me. In pre-transfer footage, my first attack tends to land with Hawk's Eye having 15-16 seconds left on the timer, whereas in post-transfer, it lands at 16-17 seconds. Already from the start, it's a big difference, for me at least. Plus my Bloodletter often clipped into things pre-transfer, and pretty much not at all post-transfer.)