It seems to me that these enormous rifles are really best suited for the USA and similar markets, where power is not restricted by FACs and such like. There, full length springs can be introduced and the power considerably escalated. I was looking at the Diana 350 a few days ago which, from memory, is a whopping great 48in in length. In the chamber there is a spacer because, for the UK market, a smaller spring is required.
The above all stated, I am keen on Diana - a manufacturer with a great brand name and history. I still have my Original 45, which performs at over 11.8ft/lbs, albeit some pellets do rather less. I am contemplating buying a Diana 280, break barrel, which seems to have done rather well in reviews, is accurate and as powerful as the AirKing (unless an FAC model is used). It is also only some 7lbs in weight and, I gather, has the TO6 trigger. The price is also competitive.
Furthermore, I rather suspect Diana will be a name of which we shall be hearing rather more in coming years: it has just been taken over and the UK Distributors, Edgar Bros, have recently been appointed.
Rgds
A