Problem with a flat sail is you get the negatives of a large headsail without the positives: heeling force, but no forward thrust. The attack angle will be wrong relative to apparent wind and mainsail sheeting angle, and it wil be very difficult to get the sail to 'set'.
I'm with Jeff on this one. A smaller sail with more powerful shape is the trend these days. Add a few means of shaping and depowering it -- magic box, jib cunningham, backstay adjuster, and moveable jib cars -- and that should give you decent performance from 5-20 kts. After that, you are on your own.
Most tubular furlers, unless highly engineered for the purpose, will struggle to reef genoas and may not survive the torque loads. They do best as all-or-nothing deployment systems. The original tube furlers on the Chrysler Bucc and Mutt were that way. Not advised to reef the jib with them.
We designed our sails relatively flat and draft-forward because we have to survive high winds on a daily basis. But they suffer in light air; the boat is tricky to drive in less than 10 kts. Goes well in forty, mind you.
It might help this discussion if we knew what boat you sail & what material you intend for the sails. Those data are kinda critical for thinking about sails. A Catalina 30 & 6.5oz Dacron is different than a Snipe & ripstop nylon.