I have replaces ballasts in two fixtures using the same GE ballast. One uses 3 , 30 watt tubes, one uses two 55 watt CF's.
Both work great since. Either i'm overpowering the 3 tube one, or underpowering the CF one, or both work the same.
I just know I got a "dead" 110 watt CF fixture for free, and for $24 at home depot have it working.