I have the 150/3 and never found it that slow but i have never tried the 150/5 so I can’t compare in any case if it is your only one then i would go with the 150/3 unless you were doing some type of production sanding at 120g or lower and didn’t require the finer orbit. I have never felt the need to go to the 150/5.

however now that I type this i wonder if the 150/5 is the better choice if you final sand by hand which i do, I usually orbit to 180 or 220 then quickly hit it by hand the same grit to git rid of the squirrel marks, it only takes a few extra minutes (or a lot!) and i find the sheen is more even…