Very strong. If you take 80 mg of oxycodone, 20mg of Opana should be just perfect, if a little heavy. It last much longer as well.
Like CH said, the ER's present a problem when snorted for long periods of time; be careful. Also, they will cause your tolerance to skyrocket, so have an exit plan.
As for the IR's - they will cause less harm when snorted, and as the pill has no insoluble binders, and they are all fairly large, it can be effectively micron filtered then dried to make a reduced powder for snorting, or simply mainlined. (although I wouldn't recommend that)