I tried series because of this tread and yes, with my magical fingers I feel the difference of torque.
(Moreover, just to thanks Ryan: I have now a 75cm*75cm*6-8cm MPCNC 525, with a 500W Chinese spindle and classic steel pipes 25mm. With a single flute 1/8, I can mill MDF with 2-3mm DOC, feedrate 15-20mm/s, plunge 3-6mm/s with a final tolerance of 0.2mm maximum. That’s a huge improvment of my first MPCNC (more than just an improvment in fact). To sum up: it works well! I still have to try other materials like plastic or aluminium now. Thanks again).