I think 6ft is too big and ambitious for either pvc blades or high voltage dc motors adapted for a use they were not designed for.
They are fine for starter projects and seem to work well up to about 4ft.
You may be able to extend pvc up to 6ft but you will need a substantial motor, probably a high grade servo motor or something with decent bearings a decent shaft and the ability to cut in at about 100 rpm. Such motors exist and weigh a ton and cost the earth. If you find one surplus at near zero cost you will be lucky.
Anything beyond 5 ft is starting to come into a different field, needing decent blades and preferably a permanent magnet alternator matched to it. You seem to have been lucky with the tower and it may be worth building something to do it justice eventually. For now for experience if you want to keep simple and cheap I would follow the others advice and keep to 4ft.
Flux