My dogs are just medium speed, but usually catch a half a dozen or so a year, by just steady pressure, Rabbits are not made to run for a long time, but fast for a short time. Alot of guys that run medium speed dogs catch rabbits. You are just going to have to watch enough different speed dogs run to figure out what you have, or go with someone who knows
I started beagling about 3 years ago and started with the fastest dogs i could find and didn't have any luck with staying on a rabbit So i got out of it for a year and just got back it to beagling in september buyin what i call med speed and just now got 4 dogs put together that i like and can stay with a rabbit and i would call them med
Most hunters that like to have long sustained runs end up with the medium speed dogs. They loose fewer rabbits. Although there are some very good fast dogs, just like driving a car "the faster you go the more likely you are to run off the road and crash"!