I have done track days with No Limits in the UK on my 790 Duke. Whilst i got swallowed up on the straights by the 1000 cc bikes at no time did I feel the 790 Duke was out classed on the bends. Another rider was on a a tricked up790 but still road legal. He went out with the advanced rider group and watching him once again he did not look up of place.
Track days are a cheaper alternative to a race bike and I think you get greater value for your money and more time on the track.