Another free M3G benchmarking test is <a href="
http://www.futuremark.com/download/?spmarkjava06.shtml">SPMark Java06</a>. Checkout the <a href="
http://www.futuremark.com/download/?spmarkjava06videos.shtml">video</a> of it in action.
Running the 3D animation gives these results:
<a href="
http://service.futuremark.com/compare?spmj06=335">SonyEricsson K750i : 4.2 FPS</a>
<a href="
http://service.futuremark.com/compare?spmj06=228">SonyEricsson W800 : 4.2 FPS</a>
<a href="
http://service.futuremark.com/compare?spmj06=329">Nokia 6630 : 13.5 FPS</a>
<a href="
http://service.futuremark.com/compare?spmj06=357">Nokia 6680 : 11.4 FPS</a>
Sadly there isn't a listing for the Sharp 903 which should be a lot faster than all of these. (and I don't have access to one yet either

)
Both the Nokia 6630 and the SonyEricssons are great for developing midlets. The SonyEricssons have on-device debugging which is always good. The Sharps can be a bit of a pain.
(I should point out that I don't have access to the latest M3G devices, these are just the ones I know, so there might be better ones out there)
If money is no object then I would suggest buying all of them.

They will all behave differently anyway.