Not 100% sure on issues with the seamless vs welded, but a max variance of .075mm doesn’t sound like a show stopper the design could not handle. I can vouch for the DW660 being pretty loud, though its performance with the rheostat has been excellent. As for the PLA question, I also live in Phoenix and my shop is not cooled unless I am in it. I hear you with the summer temps. In the late afternoon I can get readings of over 120F at the west window. That said, I have three printers plus my MPCNC in there and they are all virtually 100% PLA (vast majority is Hatchbox) with only some PETG mixed in on the printers. I have been through three summers in this shop and have only had one failure I attribute to the heat and that was on an extruder tensioning arm on my D-Bot that seemed to warp under the constant pressure from the spring. All other mounts and everything else have stood up admirably. The glass transition (Tg) for pure PLA is around 140-150F, higher for a lot of the blends we actually end up with sold as PLA.