Quick question - Motor choice.....

[Nige55]

I would really appreciate anyone's suggestions for this - I'm about to order a new brushless motor for the season coming up, and I'm not sure of which rating to go for.
From the stores that I would order from, it's down to an LRP X12 4.5, or Orion Vortex 2008 6.5 or 4.5 (No where seems to have the 5.5, which may have been ideal.
I race an original BJ4 with lipos and NimH outdoors on a faily small and tight track (on loose dirt with few carpet sections).
Do you think a 4.5 would be overkill ? Would the 6.5 suffice ? Wich would be better for a tight low grip very technical track ?
Any comments appreciated.
Cheers,
-Nige.