There is more than one way to measure the size of a roundover bit. Some folks are referencing the diameter, some folks reference the radius. If you are talking about the diameter, then 3/4 inch is not large and should be fine on even a small router, 1/4" shank. In oak, sure it will dull but that hasn't much to do with the HP. If it is the radius, then 1/4" is a bit small, and you are more likely to warp it. But you don't have to change bearings to make multiple cuts iwth a roundover, unlike some bits, just lower it in a couple of passes, that will still work with a piloted bearing. I do that all the time with 1 1/2" roundover bits, (yes, radius, which of course is 1/2" shank) But in oak, I think it is a good idea with 3/4" too, especially if 1/4" shank. If you hit a knot or something a bit hard, you risk bending or even breaking the bit otherwise.