I think we're all getting a bit confused with this BBSO1/BBS02 business. As far as I see it, the latest motors are as follows:
BBS01 motor with 36v controller
BBS02 motor with choice of 36v or 48v controller
BBSHD with 48v controller
If, for example, a vendor quotes a 36v BBS02 as a 250w version, then it's just the same as a 500w version, electrically and mechanically, but detuned via software programming. The 48v version may have a slightly different stator winding to the 36v, but this is just to change the motors RPM to offset the different voltage. Probably to keep the cadence similar between the two voltages.
Apart from the 250w BBS01, all the others aren't technically legal anyway, so why not just plump for either a 36v 500w or 48v 750w BBS02 and program it just the way you like it.
Here is an example of a BBS02 500w kit, which is basically a 750w version detuned to 500w. The motor and controller is exactly the same in both units!
http://eclipsebikes.com/product_info.php?products_id=5
Note: posted at silly o'clock in the morning, so may contain technical errors