I've used 09, 10, and 11, but my guitar always ends up sounding way too muddy when i try to go too low. C tuning has never been possible. But then again, it is a horrible guitar that buzzes a lot even at E standard.
Hopefully getting this Ibanez repaired will fix all my tuning problems. Though I'd still like a 7-string so I can learn Dream Theater and Nevermore properly. They just sound shitty an octave higher.