Trial and error, I suppose. The V3 puts your neck in a more natural position than either a DF or a reclined high racer, but as BP says, it's hard to predict. More reclined than an Easy Racer, though.
The V3 is supposed to climb well, and while I haven't put many miles on one, and the relatively few miles I put on one didn't include much for hills, but they seem very fast. Randy ??? (the owner) told me he thought the V3 seems to be equal to pretty well any high racer given the same "rider power!"