yeah, all of the above, but don't forget about technique. I'm coming back from nearly a year off the bike and I don't yet have my strength back. But I can ride pretty fast if I emphasize technique- pedaling circles, high cadence and AERO AERO AERO. If you care about riding fast, then ask yourself if you can ride in a more aggressive position without hurting too much. Flip your stem and get down in the drops. Not only will you have less wind resistance, you'll also engage different muscles to help your effort.

But don't make too many positional changes too fast. Do it gradually.