With QCTP's there are trade-offs, like most other things. Bigger is more rigid, but is more cumbersome. Rigid can be better, but if the lathe isn't sturdy enough to take advantage of it, there is no payoff.
50 years ago, we were using brazed-point carbide bits on WWII-era machines. A 1/2" bit was tough enough to use on a 20HP lathe, and with flood coolant you could take 1/2" off a side using 1140 steel. When insert bits became affordable, the bits and holders got larger, and there was an increase in productivity, but not a spectacular one. For a home shop, the trade-off is more about getting the bit properly aligned with the work than taking the most material in a cut.