First off, don't wait for Winter. Get it done while the fire is still in you. Stuff happens and things don't get done. Better to move on it now rather than later.
And in regards to the "variable speed", I think it's a good idea. I'm a noobie to blacksmithing but I like having variable speed. I have a rheostat controlling my blower. I can give it a low blast for a slow even heat on small stuff or crank it up for heating larger stock. It's a good idea to have as much air as you could want at your disposal.