I agree with your approach, start 6+ weeks of MTX +/- low dose prednisone (5mg). A more vexing situation is the patient who is suspected of having RA on the basis of steroid responsiveness, history and exam who have negative/non-diagnostic labs, x ray, and comorbidities with no allergic, infectious or neoplastic etiology apparent. Of course, the first thing to rule out is fibromyalgia! A trial of hydroxychloroquine for 6-12 weeks is reasonable in this scenario as symptoms permit until matters come into better focus. On occasion I have had unexpected responses to Plaquenil when diagnostic uncertainty existed. Remember monocyclic vs polycyclic clinical course of RA from the old days! When all else fails, taper off the prednisone and see what happens clinically. Diagnostic and therapeutic flexibility beats dogma, habit and non-critical thinking.