I have a Bernina 730 and am very happy with that, then last year I got an HQ Sweet Sixteen sit down. I've seen the 830 and there is no comparison in the available size in the harps.
My HQ is sixteen inches between needle and pillar, BUT it also has 8 1/2in between the table top and the underside of the machine, so I can stuff the biggest quilt in that space and still have lots of room to manouvre. From memory, I would doubt if there is more than 5in in that measurement on the 830. I still get to sit down at this machine, it comes with a roomy table, but takes up a far smaller space than using it on the conventional long arm frame (but you can still upgrade to that in the future if you have the space).
If it were me, I would go for the HQ, and try to get a good used Bernina with embroidery package.