It really depends what gearing options you have. Crunch some numbers using
BrianGs speed calculator. If you can reasonably gear a motor with 40000rpm. Go for it, but it might run hotter then a motor revving at 30000-35000rpm. If you want more runtime and lower temps go with the higher wind version. Either on 10s or 12s A123.
Wheight depends on how much does a savage roller wheigh? Wheight of your electrical components is easily calculated. Wheight of your desired tires really can make a difference in wheight. I never converted a savage, so i can't tell you.