Warrior General Games

By keeping him shorter, he gets the +2 spd boost. I'm not sure how big a deal a WR's height is, but it seems to me I'd rather take the spd boost at the expense of height.

Wes Welker is 5'9" and that's working out pretty well for him .

he gets a +2 agility boost...

Smaller players accelerate faster but don't receive as well.
Beyond a certain point I don't think it matters much.

Hope you can jump!

Wish you were a little bit taller, wish you were a baller
If you were a girl, with a phone, I would call ya

If you had a rabbit in a hat ...

If you're building a WR who is going to take speed very high and you are planning on getting all your yards by separating from a CB, than 5'8" is fine. Unfortunately, jumping (and height) seems to be the only way WRs can gain any sort of advantage in the receiving roll as catching seems to be negated easily in the form of deflections thanks to the CB's largely superior agility and vision rolls.