Lets start with the headstock bearings, the heart of a lathe. The SB has sleeve bearings like a precision cylindrical grinder. Granted, the spindle bore could be bigger but it will easily accommodate 1.350 barrels, a common size for rail guns.
The entire headstock is one big heavy casting, hence, rigidity like no ball or roller bearing lathe. Most small modern engine lathes have the headstock made as a thin waled box and many except the very expensive have cheap spindle shaft bearings. You can get a Monarch EE with great roller bearings, but replacements were $18,000 in 1992. That was the last EE's I sent to Monarch to be rebuilt before I retired.
You will hear quite a bit about chamber chatter or thread chatter. This is caused by that thin-walled box headstock.
Granted, too that the SBH 10 is no longer made but there are thousands of them parted out at used machinery dealers. The US Navy alone bought tens of thousands to use on=board ships since a SBH 10 can be easily broken down into small components that only weigh 100-150 pounds each.
Call most of the top quality benchrest gunsmiths and they will have at least one Heavy 10 in their shop to do the precision stuff.
A reminder, when the Heavy 10 was discontinued just a few years ago they sold for over $16,000.
As to the Heavy 10 vs a 10K, the 10K has a spindle bore of about 7/8" and a much smaller headstock shaft and bearings.
I could go on but I think you get the idea.
