I can't help you with the brushless questions (sorry!

)
but in regards to the 6 spider versus the 8 spider, here is a thread on the UE boards regarding the differences:
http://www.unlimitedengineering.com/...&threadid=1867.
Personally, I'd take the 8s, especially with the off-the-line torque of a BL motor, you don't want to ruin the day with a broken diff.
On a side note, Isin't CEN releasing a 2 speed for racing?
*Edit: I was thinking about getting that servo (HSR-5995TG). What is this programmer you speak of? Something you need to set the EPAs of the servo?