@Reefsider, I'll just offer some small things to think about. Regarding 2 motors vs 1, you've worked with a few industrial machines by the sounds of it, have you ever seen 2 motors driving one belt? I'd have to guess not, and there is a reason for that. Ask any I3 user and they'll tell you their 2 Z motors can get out of sync, only imagine those two steppers were tied together, they'd be fighting each other. That and they'll be fighting each other all the time since their steps and microsteps wont be exactly the same. Just use one bigger motor. I can't think of any application where motors are coupled together like that.As for cable drives, they've been done before, and I'm a fan of them. That being said, the reason to use them is generally because they are cheap, or because they can be routed in 3 dimensions which isn't really useful in a delta where you need one straight back and forth loop. String drives also have a few issues to deal with, specifically pulley walk (where the string winds up one side of the pulley as it turns in one direction, and then walks the other way when the pulley turns the other way). This isn't an issue in steering systems where the pulley doesn't rotate too many times, but on a 3d printer the drive pulley makes a lot of revolutions from one extreme of the axis to the other which means the string will walk a lot. The other is triangulation error, strings are often routed (or end up due to pulley walk) at a slight diagonal which can cause minor cosine error. The triangulation error is mostly at the extremes of travel where the carriage gets close to the pulley (which you wont use much on a delta), but even then isn't huge. The final issue which I think is overstated is slipping, cables don't have teeth like belts and can slip. That being said with a couple of wraps around a drive pulley you'll find the stepper will skip steps before the cable slips on the pulley.Also, I'd second CA's suggestion of using wheels. A delta that's moving fast, especially in a zig-zag type of way like for infill will have a fair bit of vibration. Linear rails are pretty shoddy at vibration damping, it's one of the reasons subtractive machines tend to use box or V ways instead.Have a look at nicholas seward's builds, they're fairly exotic as far as their mechanics go, but he tackles a lot of the issues cable drives can have. I don't think he's eliminated the issues I've mentioned in any of his machines, but focused more on making them so small that they don't matter realistically. There's a few solutions that completely fix the string walk and triangulation issues I could point you to if you decide to go that way.