Well there is a $5,500 price difference between the G0670 and G0509G. That's enough to buy a high quality motor, replace the electronics, buy a DRO, a Dorian QCTP and tool holders, and probably a rotory phase converter. ;-) Made in Taiwan does not guarantee 100% made in Taiwan. In my research I came across some supposed made in Taiwan lathe (not Grizzly) where the castings were actually made in China.
I just finished a detailed comparison of the specs on these two machines vs my G4003G...
1. The G0509G 4HP motor requires a 30 amp plug and is rated as drawing 17.45 amps full load vs the supposed more powerful G0670 5HP motor which requires only a 20 amp plug and is rated 15.7 amps at full load. Something fishy there.
2. Floor to center height arrgh the G0670 wins that one at 44.25 inches vs the G0509G at 47 inches vs the G04003G at 46.25. I was hoping for a shorter height as my G4003G is about 4 inches too tall for me. So I'll be building a work platform to stand on.
3. Number of feeds is 17 for both the 16x40's, far fewer than the G4003G's 40 feeds. But then I only use like half a dozen feeds so meh.
4. Carriage lead screw diameter is about 1.2 inches for both, vs .870 for the G4003G so beefier.
5. Carriage lead screw length is 44 inches for the G4003G vs 54 inches for the G0509G vs 61.5 inches for the G0670. I kind of expected the two 16x40's to be about the same. Best I can figure is the tailstock on the G0670 is longer requiring a longer bed to achieve the specified 40" between centers.
6. Carriage travel is only 33 inches on the G0509G a bit disappointing vs 40 inches on the G0670 so 7 inches more hmmm...
7. G0509G swing over the saddle must be a misprint, its only 9.875 that's less than the G4003G's 11+ inches and way less than the G0670's 15+ inches. I'll have to confirm.
8. Spindle length on the G0509G is 5 inches shorter than the G0670. I know shorter is better for gunsmith work but the wider G0670 is probably more stout. I did confirm the Go509G has a 3 bearing spindle, 2 tapered and 1 roller.
That's about it, no show stoppers for the G0509G though the height is annoying. Oddly the brutish G0749 with the 3 inch spindle bore, 10HP motor is only 41 inches floor to center, the lowest by far.