While I haven’t chronographed your exact load, I have run the 124 gr MPHP (pre nuke) out of a new Glock 48 with 3.6 gr of Titegroup and S&B SPP. They clocked an average of 949 fps with a Sd of 10.
According to Glock, my barrel is 4.17” long. I suspect a 4.0 gr load would top 1,000 fps, but probably under 1,100. I should try 4.0 just to see what it would do, already have 3 primer tubes full of CCI-500 primers ready and waiting on the Dillon RL-550B.