Im not sure its worth getting that complicated (small gears first part of the season, big later, or other way around).
I always describe the bike sessions as a way to get the high speed, high intensity training without using up your energy 'getting' there. In that sense, I generally go a bigger gear since Im not going to tire myself out with the 0-50kmh part, and just get the 50+ stuff. If I want to spin to 150rpm, I don't need a moto for that. I don't need a track for that lol.