Hi,
what is it that you are trying to improve?.
Most 34 size motors have quite high inductance and consequently do not do well at speed, in fact often the 23 size motor with low inductance will
out-perform a 34.
If you really want to step up get AC servos. 400W servos in 23/24 size would be perfect, more thrust, way WAY faster and HUGE overload whereas steppers have none.
Have a look at DMM (Canadian brand made in China) or Delta (Taiwanese made in China) which are two good brands with excellent backup, good documentation and
most importantly good and free set-up an tuning software at very fair prices.
Craig