TL;DR: When/where should we have our daughter start at her new preschool?

We were accepted to a full-day preschool where our daughter has been on the waitlist for almost 2 years. We would admittedly like to move her sooner rather than later. Here is the caveat: She turns 4 in June. The school transitions all of the rooms in August.

She could start in the 4's room and not transition in August.
-or-
She could start in the 3's room and transition in August.
-or-
She could start in June in the 4's room when she turns 4 and stay in that room during the transition.

My thoughts: if we put her in now, she should go with the 3's even if it means transitioning late because she will then transition with her class. If we put her into the 4's class, she would probably be upset when all of her friends leave her to go to "real" school (and graduate) and she has a whole new class of kids to meet. She's smart and catching on to things that would move her up soon in her current school (which moves kids according to skill level) so keeping her in the 3's room at the new school might be boring for a while? But at least she would be with the same class.