Factory VFD machines are usually 2-3 speeds, the motor are often the next size up to handle the RPM extremes. I do find that adjustment on the fly is advantageous for things like boring/drilling where there is a sweet spot. Also when you cut down in diameter you often turn up the speed to maintain SFM. The soft start, slow jog and electronic braking are all worthwhile. Just like using a DRO, died in the wool say it is one more thing to go wrong, those that use them always say I should have done it sooner. Nice to have, but not a must have.
As far as things breaking/longevity, I have yet to see a VFD fail in 10+ years other than the cheap Chinese brands. People are still using VFDs that are 2+ decades old and pretty darn big. They all work pretty much the same, they are controlled by programmed inputs and that isn't going to change in the near future. I will probably be long gone by the time my VFD goes south (the rated service life on the Yaskawa's is something like 27 years). In the mean time I get to enjoy all the benefits of the VFDs. Eventually it will be cheaper to have these mechanical machines electronically controlled and eliminate gearboxes, change gears, etc. to a major degree. My factory VFD mill is a direct single speed belt drive, with just a back gear, all the controls are electronically controlled. Yes, I think VS is worth a small premium, but it is the rest of the machine that is determining the decision.
You can compare numbers, but at the end of the day until you start getting your hands on a machine it is hard to appreciate the differences. You also need to factor in that the lathe accessories can cost almost as much as the machine at the end of the day. You want a D1-4 or D1-5 chuck mount, the latter is required for the larger spindle bore, chucks and back plates are available in both sizes. Most people end up with a 3J scroll, 4J independent and usually some form of collet chuck for smalls. Some lathes come with chucks, the Chinese mainland chucks tend to be poorer quality so you may want to get better chucks. Get a QCTP and a buch of holders. Most of use use a BXA size QCTP, which is a very common size. Bigger machine may need a CXA (next size up), 1236 might fit a BXA. Size matters as to availability of tooling. It is a deep rabbit hole from there, and a long learning curve.
Probably focus on the 1340GT, 1440BV and 1440GS. Capacity wise they are all close, the 1340GT is the most popular. No change gears other than for metric, the Norton gearbox is primitive but has been used for decades. Fit/finish is significantly better, but a few less features. My major concern with the 1340GT was the lack of braking, this was solved with the addition of a VFD that will stop the chuck in 1 second.