I just hit level 3 on the SL8. I'm probably going to work on the Aethos and the Cadex Tri (alternating based on which is appropriate for the ride I want to do) next. Then probably do a low level Specialized bike to get the Specialized Halo bike (the most aero in the game when fully upgraded). Since upgrading that fully (and getting it) will probably take over a year (and they'll change things in that time almost assuredly), I'm not really making long-term plans.