Difficult question to answer.
Let's say you're working with a Teebird. You could get your throws with the Teebird out to 350', then try a faster disc from there and probably see an increase in distance, so 350' with a TB is enough things going right that you can get some utility out of a faster mold.
However, 350' with a Teebird is not at all pushing what that disc is capable of, so at that distance you aren't maxing the disc out and you don't need to disc up to get more distance. There is nothing stopping you from learning to throw a Teebird 450' if you really want to.
The question is more or less how much time and effort are you willing to put in to increasing your distance? That is what it will come down to. Some people don't ever drive with a putter, some of us are not satisfied with driving a putter less than 400'. It's not a question of what the disc is capable of as much as it is a question of what you are willing to be capable of.
I've always found this to be an interesting and controversial concept - what a disc is "capable of"
Theoretically a disc is capable of infinite flight...but it's the thrower that has the attributes of capability, not the plastic.
I think a more useful way to put it to the OP is like you're saying: how much time can you dedicate and what are your goals? 400' is humanly possible with a Teebird no doubt, but if you're not playing on the pro tour is it necessary?
Food for thought