Well anyway tell us about your flat 50s as soon as you've installed them!! :D
Well, it's early to give final conclusions, played guitar only half an hour or hour, but first impression are:
1. Neck pu is less output than stock, and more airy and open sounding, closer to Strat I think.
2. Bridge are not ice-picky or harsh, more growly than stock, but I didn't find him bass and mid-heavy - that sometimes can be dull. Also output is pretty the same as stock.
3. Both pu have TWANG - fat, quite warm but not overly mellow, liked it a lot :)
Now I'm going to fiddle with pickup height - it makes a lot of difference with BKP.
Interesting thing - pickups arrived in old-styled BKP box (not glossy, without graphics, with BKP logos and etc glued and not imprinted), and there was an only two options - flat 50 stagger, and 55 stagger. Could it be that I got old 50s (now it's 52s)?
But mine have steel baseplate, and 52s have copper plate.