I have the smaller stradic 2500 with 8 on it and it's fine. I bet 12 will be ok too. Give it a try...
Was recently taught ( after 40 years fishing intermittently) how to load a spinning reel correctly - will pass along should it matter. you want to take the line off the end of the spool so that the way it is coiling off matches the way it coils onto the spinning reel. If you set the spool on the floor it works pretty well. if you get it right, loose line will NOT coil up on itself in a mess. If you load it against the twist, that's what will happen.