I don't think anyone has made a comparative benchmark of C2/Starling (first time I personally hear about Starling).
You can always check this blog article
from a few months ago that might give you some informations about C2 performances.
In the absolute I can't say if C2 performs better than Starling, but it sure does perform well enough.
Before buying, just build the same project with the free version of C2 and with Starling and do your own benchmark test, it will probably be the best way to answer your question.