I would get a sprayer that you have parts and service support close to you.  I had an 854 and treated me well, but always had concerns of wheel motor issues.  I’m now running a Case 4420.  If you plan to spraying any corn fungicide, you want to look at a Hagie.  The newer series from the 854 went to a different system and wheel motors weren’t a common issue.  I saw a post a while back that told the model numbers for the better Rogators.