Hy Allan,
I have seen both mills in the real world and worked on one similar to the G0519. Concerning size, they both are monsters. The G0519 is not far from a bridgeport in footprint (table size is the word here). Go to an outlet and take a look, this dampens the shock the day the machine arrives.
Please think about the maximum size of work you want to do before you decide. The working envelope is bigger on the G0519, the manipulations that can be done are nearly the same (x and y travel, swivel head left and right, but the G0519 can´t rotate around the column). Another point is x-y- table size, consider a rotary table with 200mm dia, you´ll need that! Otherwise, clamping the bigger parts is no fun at all.
However, the gear is a big time saver. You don´t even need a VFD( but it´s more convenient), you can also go with a tapped winding motor. This enables speeds up to 2500RPM (with full motor torque).
Then, the quill travel is longer on the G0519. This is nice for deep holes in angular drilling operations ...or cutters with differing length (read again and think, this is very important!). Or concentric drilling operations to the same center, like valves and valve guides in one setup. They´ll never be okay if you have to do it in two steps. Concentric drilling is mandatory here. No need to touch the machines head, on the G0519.
Another thought for a round column mill drill: It´s no problem to attach a keystock precision square rail to the z-column and machine a cutout slot in the head that can use a gib. I´ve seen this on different emco FB mills. This denies rotation of the head while altering z-position.
But this still leaves you with the problem that the angle of the z-axis ist fixed to the table, which is a pain in the back in case you have to make more than one angular drilling operation in a precise manner.
Not to mention that there are models similar to the G0519 that allow you to turn the table sidewards by up to 40 degrees. It´s a nice machine.
Also, it´s easy to cnc it.
Before shopping, put both catalogs side to side and compare and imagine which part can rotate or move in which plane and what it means to machining. Also, take a few difficult parts from the mini mill and try to imagine how attach and run them on your favorite new mill.
Cheers,
Johann
Ps.: I lean towards the G0519, because I´m familiar with this machine.
I have not worked with a 6x26, but I know a very satisfied owner.
I guess both are good machines.