If that's the case then I really don't need a proportioning valve as long as I don't jam on the brakes and try to stop on a dime.
Not necessarily. Without a PV, you can have one set of tires lock up before the other. That can cause a serious handling problem. Even if it only happens during a panic stop, it's still critical. Rmember, you MAY have to stop on a dime . . .

On a custom build, the only way you can tell whether or not you need a PV is to try it with (or without) one and see what happens.