Fortunately for you, aftermarket wheels that promote fuel efficiency are generally also good for performance because they weigh less than stock. Less unsprung weight is your friend.

If you have a 5th-gen (like me) I would get 15" rotas because they are even lighter than the Si wheels (most of them) and they look fantastic (imho). If you have a 6th-gen civic then I would get either 15" or 16", but I'd probably still stick with 15".

To retain stock size on a 5th-gen with a 15" get a tire that is 195-50-15
To retain stock size on a 6th-gen with a 15" get a tire that is 195-55-15

If I've posted any incorrect info, someone please let me know.

P.S. I have 15x6.5 rota slipstreams and I love them. My tire size is 205-15-15.