I wrote a simulation about a year ago and yesterday was the first day they showed F9 S1 reentry data which was really useful for me to see how wrong I was. Although, I never tried to boostback but only tried to recreate the ballastic reentry on a drone ship landing. It still has it's issues as the flight is about 2 minutes later than it should but I can run the sim and find dynamic pressure along a ballastic trajectory with a similar degree of error....it's just a bit difficult to orient, burn, and land in the right place for me to do alone for a RTLS trajectory.
Crosschecking my data I had max speed of about 2300 m/s before the reentry burn(but keep in mind, ballastic trajectory with a drone ship landing-no boostback burn at all to kill velocity) and the reentry burn reducing it's velocity to about 1200m/s which is 200m/s slower than the RTLS core when it starts it's reentry burn.
I found the image from my pdf that I was taking these numbers from. Time starts at 0 with MECO. The weird stuff at the end is due to the fact that my stage was holding an angle of attack and instanteously changed its AoA to 0 to begin it's landing burn which if I remember right isn't simulated because that's not really what I was after.
A graph of it's trajectory
It looks like the forums are nuking my x axis but if you view the images on imgur they look fine.
What's really neat about supersonic retropropulsion(That really cool shot of the reentry burn) is that the exhaust actually creates a shockbarrier wider than the rocket itself, artificially increasing it's cross-section and the amount of drag it experiences helping to slow down the rocket even further. Every bit of fuel not spent slowing the rocket down helps putting a payload up there. It's really cool stuff.
I never thought about adding dynamic pressure to the sim so I'll work on that and try to get back to you with numbers, but they will definitely not be 100% accurate. I was only looking at maximum heating as a function of v^3 to try to find a flight regime that lowered heat without expending more fuel.