When I said least restriction, I didn't mean no restrictions, I meant generally the least restriction that will perform how you want. Whatever that want is.
Eg. Say 650 gives you everything you want a 750 would only gain a couple of hp and a 500 kills 20 and gives a similar experience driveability wise. To me the 650 would be the least restriction that gives you what you want, but now lets say the 750 actually gains 15 hp across the meat of the powerband but gives up some driveability, now some wouldn't overly care about the driveability so the 750 is the choice and for other on the same combo would prefer the 650 but there's no reason to choose the 500. The choice is depending on what's needed/wanted 650 vs 750.