What i should do with that pidgeot?

With Steel Wing he isn't much use for attacking gyms. Just put him in a gym.

I don't imagine it'll be worth it to pump stardust into a different Pidgeot, so keep that one and, like Cool Cat said, put it in gyms. Always listen to Cool Cat, kids.

Meh, not like you're not going to find another Pidgey. I transfer all except Wing Attack/Hurricane, personally

Id transfer it personally Im not a collector tho

I'm level 30 and for some reason (probably my completionist streak) I always have at least 1-2 of each type of pokemon I've ever caught in my inventory. I currently have 2 Pidgeots with >1600 CP. However, I haven't used a Pidgeot in a battle since I was level 15. Keep the Pidgeot if you want, but I doubt you'll ever use it in battle.