I went with the RCgear shop 3900 kv for$29 at Tower and the Raider BLX ESC. It is plenty fast ..... and thats on 8.4 nimh.
Mine is the original mega not the XL so yours may be a tad heavier but that's what I would recommend for a "budget" upgrade to brushless! (That ESC may only handle 2s). Some of the other guys may be able to chime in on that.
Planning to do the same on my new mega 1/10. Curious what gearing you Rdub? Was thinking I'd start somewhere around XL BLX range 54/57 and 17/19 in 32p.