I've had more of a chance to hit with mine in the last few weeks too and am still liking it.
Playing back to back with my old Speed IG MP 315 16/19 I noticed a slightly hollower feel with the Graphene Speed Pro on hard groundies. But after a while just playing with the Speed Pro you get use to or just don't notice it. It also feels slightly stiffer than the IG MP but not by much and I haven't had any arm problems.
But back to back it feels noticeably more manoeuvrable than the IG MP, particularly at the net, and so much more stable off centre.
As for groundies I'm finding I can hit some very hard and flat forehands very deep into the corners that just skid on. The first time I managed to really pull one off the guy I was playing against said it was like trying to chase down a flat 150kmh serve.
Spin is still surprisingly good for such a tight string pattern and it gives nothing away to the IG 16/19 maybe due to how easy it is to just whip the racquet head around.
Serving is a breeze and it is the control I am loving but still not giving much away in raw speed. With the factory string I was probably getting close to 190kmh on the hardest of my flat first serves and I've been able to get some deep second serves to kick quite high.
Another big test has been playing with my kids using the low compression orange and green dot balls. One thing I hated about the IG MP was that slightly off centre shots with the low compression balls would just die or be hard to control. With the Speed Pro I've found that it is so much easier to control and keep the ball in play, particularly when I have to volley wayward shots when playing the half court with my youngest son.
So after a month of playing with the Speed Pro after having tried a few different styles of racquets since returning to tennis last year I think I've finally found something that really suits me. Although no doubt similar specced 18/20 racquets like the Blade 98 and EXO Tour 100 would be good too.
Also I'd all but killed the factory strings I restrung it with some Sonic Pro 17 @ 50lbs a few days ago but have only hit with my kids since then. I've got some Sonic Pro Edge on the way that I am really looking forward to trying out as from some reviews it sounds like a perfect match for this frame.