Well here's my opinion, and the answer is affected simply because I view agility backs to be inferior to speed backs. I'd say have all the equip in speed. 55 is nothing, that's literally at a crawl in a pro league and he's probably slower than his LOT. You're right to be concerned about it.
You simply can't build a slow "Fake/Agility build" player and expect him to do well, even with 100 agility and a lot of SAs, he's going to get annihilated just because there will be so many opportunities for faster defenders to tackle him. If he really wants to stay agility-heavy and find a good balance, I'd recommend either of the two higher speed options you listed.