It doesnt matter - you can choose to learn to ride with 4:1 depower on your existing TT gear, to get used to it.
And you can learn to ride the Sector without 4:1 depower to get used to it.
You can also do both, and just not use the 4:1 depower much
If I were you though, I would start riding the Sector first, and learn how everything works and what the ups/downs are regarding power and apparent wind etc etc.
Then when you got some experience, you can get/make a 4:1 depower and use that