I'm sticking with Unity also.

Good choice IMO. Apart from potential performance pitfalls, Unity is more or less on-par with Unreal (or will be again when Unity 5 comes around).

Stick to some good advice you can find on the Unity homepage, and on the pages of some longtime Unity users, and you will get a decent performance even with more performance hungry projects.

There is a whole chapter of the Unity Documentation found on the Unity page dedicated to performance optimizations. Read it and remember it.

But only after you a) finished your project and still have time to polish it or b) run into show-stopper performance problems with a mandatory feature (one you cannot just drop).