I think it the answer comes down to what do you want to make? If you are only going to make metal parts for 1/24 and 1/25 scale models then the 7x and 9x will be plenty big.
The next question is: Do you really NEED a CNC lathe? CNC is great, but it does have a great learning curve over running manual machines along with the greater monetary expense. If you buy one of the generic mills or lathes, there are kits out there to convert them which makes it easier than trying to convert an odd ball lathe or mill. But there is still a certain amount of troubleshooting that needs to be done even in converting a generic mill or lathe.
In my case, I build 1/8" scale military, old west, and Civil War miniatures. My first purchase was a 7x lathe and then the x2 mill. I CNCd the mill first because it was easy and I had a few parts that I needed to make multiples of. I eventually bought an old 1940s 12x36 Clausing lathe to replace the 7x because some of the parts I needed to make were too big for the 7x. Now some of the parts that I need to make on the lathe are in multiples so the old Clausing is getting CNCd. (Long story on why I decided to CNC the old Clausing.) The way I am doing it is NOT the way to go. The Clausing does not have a kit to convert it. I've shopped eBay almost every day over the last two years looking for those great deals. The good side to this is that I will have a CNC lathe that I built and will only have about $2500-$3000 in it (granted...if I can get it to work...there are some logistics to work out with a conversion like this...lol). I couldn't buy a new 12x manual lathe for that money and then I would discard much of it CNCing it anyway. I'm only using the bed, the headstock and the tailstock on the Clausing. The rest is going on eBay to recoup some of my money back.
Here is my lathe retrofit:
You had posted a pic of a overhead belt drive lathe that you were asking about CNCing. I wouldn't even do that to it. I'd buy it just to have it down at my shop for a conversation piece though. How close are you to South Dakota?
I'm now starting to look around for an 45 series mill to replace the puny x2. The 45 will get the CNC treatment of course.