I'm in a similar boat, and getting my mids out to 250-270, and drivers out to 290-310, so I can relate.
I've recently started focusing on arm speed, and specifically trying to throw faster instead of harder. Without even holding a disc, I'm swinging my arms back and forth and trying to go faster and faster.
It seems like the only way to go really fast is to squat a bit, and use the legs and torso muscles to propel the relaxed arms around with a specific timing, which seems to match what I've been reading online for months now.
I find it hard to grip with the hand and control the wrist while using the legs and torso so aggressively and letting the arms be relaxed so the throwing arm can whip around.