Why the rush for the full M?
The only difference between the M2 and the M is a 0% blood alcohol content while riding. I don't believe there are any significant insurance discounts between M2 and M, at least not with the company I was insured with. And of course, no restriction on the kinds of motorcycles you can buy between M2 and M.
Maybe some dealerships won't let you test-ride a bigger bike without a full M. That's all I can think of.
You can get an M2 60 days after you pass your M1 written test.