I own a 4" Speed Six and GP100 sixguns in 3", 4", and 6" barrel lengths, including fixed-sight 4". The 4" sixguns are carried and used regularly. The only difference I see, from a practical standpoint, is that the Speed Six is just a bit less bulky than its GP100 counterpart. I think there is a slight weight difference, when comparing the 4" Speed Six to the 4" fixed-sight GP100, but it is so minor I don't notice it. My old holsters once used to carry 4" K-frames will accomodate the Speed Six, so it sees a bit more use as a belt gun, whereas I tend to carry the GP100 in my Safepacker. If you own neither weapon, the 3" GP100 will tend to be easier to find for sale. Speed Sixes are coveted by collectors and by serious sixgunners who want them for carry, and nice ones offered for sale tend to go quickly. For now, my Speed Six wears a Pachmayr Compact Professional grip without the finger grooves, and with an open backstrap. My fixed-sight GP100 wears the factory stock rounded grip. Both are a good fit for me. I have considered custom wood for the Speed Six, but that is a someday thing, no hurry. I know I have done little to help decide beween the two; bottom line is that both are very, very good weapons.