The thing to do with your collection of spindles is index them ...
hahaha! yep it did cross my mind man but i tend to use the 2000W spindle for almost everything i do and changing spindles is a moment of a job

How much difference do you think using the two double row bearings made versus one? Mine has one double row and something like (can't remember) 5 standard bearings.
i havnt cut anything with the new one yet jonathan, i was well happy with the old one, i belive it could out perform my machine with the single double row in it but as i was building a new one it seemed silly not to add the second bearing if i could suss a way of keeping the resses perfectly true.... it was a nice surprise when i fitted the shaft and there wasnt any extra friction due to missalignment (its a tough nut to crack)

it will be interesing to see if there is any inprovement but im sure the resonance paterns i get are from my gantry sides