Ours are 600's, which really hold about 660 bu.   The one which was in the shop last winter should hold at least 850 now if my math is any good.  I remember seeing two or three 1200's in the HPJ back 15 years ago, cheap as heck but they were in Arizona...we decided against going after one.  There are some 800s  I have seen up around York NE....appear to be a 600 with the ends bent out at an angle.  

The weak point is the gearbox on the vertical auger.  Weak and made of unobtainium.  Our "good" one (on tracks, and enlarged) is now 100% hydraulic drive with no gearbox.