in my opinion and experience the Velo box is best hands down! the versatility of the velo box is far superior to the more sluggish polo boxes (in my opinion
) although the gear ratio on the polo boxes are more suitable for a better top-end, it depends on what your finishing time and speed is at the moment! if you are at the 145km/h mark then i would say go for the velo box as it will be more suited to help deliver max power in that range, but the polo box will have a slight advantage if you are finishing in 155km/h + region. i have always enjoed the velo box and know of some rally polo's here in RSA that use it (obviously with different fdr's). how much torque are you pushing out ?