hmmm that's interresting.
keep in mind that if you have a heli setup for one type of blade, you'll have to change pinion gears when you switch to another. ie: a cp pro is setup for symmetricals, so you have to drop a tooth on the pinion if you bolt flat bottoms on it
currently I'm running 9T with CF blades.
I got fed up with how unstable the flat blades felt maybe this is because I really should've switched the motor to a 8T as I'm currently running 3S lipo battery (11.1v) after my nimh packs died on me.
Amazingly I'm experiencing significantly less crashes with the CF configuration in fact the only minor damage on the blades was due to me carrying it and accidentally hitting the idle up switch on my transmitter. (sometimes i really wish there was a trottle lock switch so you can power up the transmitter and not actually make it live until your actually on the field. Useful for those winter months when you don't want to take your gloves off to plug the battery in.
I think the best suggestion is to try both and find one that suits you, make sure to give at least 3 full flights to each configuration as that's how long I feel I take to get used to a blade configuration to be able to hold it stable consistently. Recently I'm finding that CF sym blades do alot better with a slight breeze a sudden change in wind direction usually throws me off way more when running flat bottoms due to the much lower response time, but with the CF I can usually correct well before I get into trouble.