Good stuff DJ (ILTCHDJ, IWILTD)...The screwball is comped to an opposite-side curveball, break and speed wise. In the early 80's, Frank Viola started throwing a "circle change up", which had most (if not all) of the characteristics of the screwgie, but was easier to teach, learn, and command. The key is more drag (skin) on the ball, decreasing velocity, and throwing "the circle" at the hitter, which creates pronation and produces the arm-side run-sink of the screwball.
Nowadays, it's all about velocity. The traditional curveball that I threw is a dinosaur, because it comes UP out of the hand, and good hitters can see it early. It matched up well with the circle change. It's a four-seam (straight) fastball world, at the top of the zone, and sliders/cutters on to off the plate, with velocity differential of 5-8 mph from the FB. In the day it was a 12-14 mph difference between the FB and curve/changeup.
Guys are throwing power breaking balls at 85-92, keeping their hand more behind the ball than on the side of it, short and sharp as opposed to big and loopy. The slider that I threw, which was pretty damn good (self-gloss POTD), had 4-6" of horizontal break, and about the same tilt...that's a cutter now. It matched up well with a 2-seam, sinking FB, that had the same break/tilt, in the opposite direction.
The plan is to "Tunnel", where you throw sequences of pitches dictated by the location of the previous pitch...EX: FB away for a strike, slider/cutter/ change up to the same spot, with movement and FB arm speed. Felix really had this going in the mid-teens, and at times had only 2-3 mph separation between his FB and change up...
Sorry to nerd-out, but I love this shit...