Hi,
Closed loop steppers are still steppers....they lose torque the faster you go, a closed loop control does not change that. They have similar speed
characteristics to open loop steppers of the same size and inductance and same driving voltage. They DO have improved resolution over open loop
steppers but not really enough to justify the price.
If you want genuine closed loop performance then get AC servos, they are so much faster and have terrific overload capacity that steppers just
cannot match.
I use and recommend Delta servos. I have three 750W B2 series, one braked and they are superb. The B2 series have a 160,000 count per rev encoder and is
in effect Deltas entry level model. The A2, A3 and B3 are later more expensive models but are well and truly more than I require.
I bought from this company:
https://www.fasttobuy.com/Supply-servo-system_c381
$438USD for a kick-arse 750W servo, drive and cables is good value in my book. They charged me $80USD each for three day DHL shipping from China to New Zealand
and they got here is 2 days 14 hrs...I got what I paid for.