Re: PM25MV faster than 2500 RPM spindle but with rigid tapping?
Most of the spindles I have seen have too much preload. The stock China TRB bearing and not great but should be as good as most other bearing from China. The most common cause of failure is crap in the bearing from all the grunge in the system with too much preload.
If you wash out the old grease and make sure the preload is correct and re fill the grease with something like Mobil SCH460 most people can get 4 to 5 K out of the spindle with little problem for years. You can do this with out removing the bearings.
I have seen some spindle that were just not balanced so like a lot of the China stuff YMMV.
If you really have to have over 5K for most of your milling then just plan on going to AC bearing. They run cooler and can go 6K all day long.
The performance difference at 4K is a lot more then you might think. With a 3/8" cutter the surface finish is much better and the cutter will throw the chips out much better. Its a huge improvement.
If you plan on doing a bunch of work with a 1/4" and 1/8" cutters and lots of 3D work then you will want higher RPM.
youtube videos of the G0704 under the name arizonavideo99