I agree with porkpal. Go ahead and give it a good pruning. The link you provided said it's good at repeat flowering, so I would go ahead and take the chance. Once it regrows, maybe try and keep it from getting out of control at the top.
Your situation brings to mind exactly what I went through with a Cl. Lemon Meringue rose. I didn't do my homework when I planted it and it completely overpowered the VERY NARROW (12" wide) steel arbor I had it growing on. It was way too massive for such a small arbor and always looked top heavy. When it DID sprout laterally from the canes, the whips got to be enormous, regardless of if I piched them out or not. I've since removed it, so it's history.
