they are extremely loud ! my buddie has em on his monster and it annoys me going down the freeway when im on my bike 40 ft away!i just dont think its right for the hyper it sounds good enough with termis,zard,etc.if you want to go that loud get a chopper.
On a serious note, wouldnt a set up like that just roast your valves? It seems that when i worked at a harley shop guys were having problems with their valvetrain after putting straght, unbafffled pipes on. Lack of backpressure was causing issues.
Typically its not lack of back pressure that caused by cooler air coming back through the pipes onto the valves... I would think that these pipe would be long enough to stop that, but its something to think about for sure