He definitely has better agility than speed...but I'd argue he definitely looked better and faster running with the ball in the bowl game. It seems the time off gave his knee time to heal, hence the extra pep in his step.
His run for a first down in the first quarter, I think on our first drive, showed speed enough to run this offense. He makes it through the line and he's going to get yards in chunks of five or ten at a time, and with Ameer, Cross, and the plethora of younger RBs, that's more than fast enough.
We do not need Taylor Martinez Kessel-run-in-twelve-parsecs speed at quarterback. We were spoiled with Martinez, and it was great to have that home-run threat every snap, but we're more than capable of grinding out drives five yards at a time with Armstrong.
And that's a good point about giving Tommy's knee time to heal up. People seem to forget he got his knee scoped seven weeks before his first start of 2013, and this was his level of mobility 13 months before he started his first bowl game: