Yea, your acceleration/bottom end would be great, but top end no so much.
A undergeared motor can, and will run as hot as a over geared motor because there isnt enough load on it.
I run a Orion 5.5, LRP speedo, and a TrakPower lipo (like my sig) and I have it geared at 20-22 depending on how much top I need. Its just stupid fast, and I usually run my 20T, have all the midfield punch, and top you could ever need. I can run till the LVC racing for a good 25 mins, and after that nothing is over 160, 150-155 area. All I have for cooling is the little air vent cut out on the motor side
Wiring is nice, neat, and short with a pack like the Trakpower lol, everything is so close
Its tight, but everything clears, nothing rubs. So for a 6.5 id run anywhere from a 22-24 and just mess around with it. But say 17 is to small.. At least run a 20