Giant lower fins and canards aside, a 36" Iris should put you around 85'/s on main deployment.
But those fins are going to have an exaggerated effect on the lower body assuming they remain together when the rocket splits on apogee. It would be interesting to see the altimeter data on decent to see what rate you are getting as well as that elusive ground based decent video that I never seem to capture.
You want to insure that when the main deploys, the rocket is in the correct position so as to avert a tangled chute, or the main getting tangled in the booster fins etc... For such a large vehicle, I would definitely go drogue.