Managing Peak Motor Currents with Capacitors
I don't see any benefit in using 250V capacitors if the supply voltage is only 90VDC, it's waste of money. I have installed Sanyo Denki motors with RTA drive, where in manual says: $$C=\sqrt{N}*C_{min}$$, where N is the number of drivers and $$C_{min}=4.7mF$$, therefore approx 8 mili farad is required.
http://www.metalwork.it/download/manual/PLSAME04.pdf