at 3.7v, i suggest you should use pinion/spur of about 28/97. otherwise your speed is not that fast. (maybe slower than your last setting of 3.7v+7.5R@30/95)
at 6.6v, your current gearing is much faster than your setting last week.
If you want to save your pocket, A123 is the best option. But the trend is using 1cell lipo without booster. LRP SXX TC Spec Ver 2 is the one which can support 3.5T. Very attractive. I saw a guy selling a brand new SXX TC Spec Ver 2 at RC EVO a few days ago. want to get one but need to get rid of my Novak Booster first.