I do not use roller furling myself, but the headsail I find most useful is a 135%. I fly it with full main in up to about 15 kts, where I start to reef the main. For social sailing, the boat will move freely in that sail combination if 5 kts is blowing, and is optimised in about 10-12 kts.
Most roller furling users I know have either a 130 or 150; those in San Fransisco say that 150 is too much, but elsewhere I have not heard that complaint; I hope someone with roller furling chimes in as I can not say any more.
My mast is flat on the sides and the same cross section along its length, I can not send a picture as I am moving everything I own... But if I come across my measurements in a box I will post them for you.
You could look on the archives at
www.sailnet.com as there was a discussion of roller furling there in the last year.
Gareth
Freyja E35 #241 1972