I can't really speak to first runs and whatnot, but if going by my 172g Blue Shock is any measure, flat tops are amazing. On a big flex line this disc might end up being my longest disc if I ever actually tested it out like that. This thing is a bullet and has surprising glide for how well it beats wind. I use this Bad Larry anywhere from 200-350. Obviously the shorter distances are on some very specific shots where I need that hard fade or a big skip, but the flat top is absolute money. Any time the course has a right turn built in, this baby comes out and dominates it.
In short, flat top Shocks are the bee's knees. Flies exactly like what I wanted buying one. (FH at least, don't have good enough form to throw it BH)