Well, CT18 & 75 summed it up best (& Dave too). But I'll add a little to the bigger blade if possible, if not wings answer. Bigger blade AND wings. If you do get the bigger blade, keep the other as a spare and set up hardware for the wings that are going on the bigger blade, then you can interchange them if you should need the back up. Good luck.
If you don't want to spend coin on a new blade,you could rework your old one.A lot of blades all use the same harness,a-frmae etc,so they will usually handle the larger blade OK.Check first to see.If you are handy with a torch and welder,you can make them yourself,or find a welder to do it for you.I have done lots of them,and they hold up fine.Here are a few pics of a removable setup for a 9 ft western (is over 11 ft with extensions on),and one of a snoway 6.5 ft permanently extended to 8.6 ft.
I read an article in a landscaping mag about 3 years ago. It tolds of a contractor in CT who had made Fisher 8 foot blades into 10 foot blades. He claimed that the weighed significantly less then a 10 footer from Fisher. His were permanent though. He had been using them for a couple years and had no real problems. I will have to find that article.
~ Guess what your banker or finacial consultant would say?
Okay, option #3 (Here's where this forum is priceless)
Buy a 9' cutting edge (bolt pattern the same, but double check.)
Bolt that on and add 12" HMWPE (High molecular weight poly ethelene: fairly common, cheap product.) to form your plow face and bolt it to the cutting edge and face of plow. It'll bend to form the same curvature of the plow.
Total cost: $300.00 cash. 2 hours time.