Mig welder suggestion

Tractor supply usually has the 140amp hobart on sale,may be to small for 5/16 in one pass...Their 190 amp is on sale right now...Here the links 140 first:
http://www.tractorsupply.com/en/store/hobart-handlerreg;-140-mig-welder

http://www.tractorsupply.com/en/store/hobart-handlerreg;-190-mig-welder-spool-gun-ready