When I bought my Benelli 750/6 some years ago, it had a stainless steel (six into six) exhaust fitted, together with a receipt for £1,750 in the document pack for it. At that time, Silentium's were not available (these were the original fit) although later on a new batch were made and I bought a set.
I was absolutely amazed at the weight of the stainless items when I removed them, I quite literally could hardly lift the full set ( I am 6'1 and was then around 15 stones). Fitting the Silentiums released a whole lot more performance (I had thought the bike a little flat, however as all of the mechanicals and electrics checked out OK and the reputation when new was for fairly lacklustre performance, had accepted that this was how it was) that I assume was down to the reduction in weight and, possibly, more suitable tuning of the standard exhausts to the engine.
I offered the stainless items for sale, with a warning of the weight and the buyer was equally astonished when he came to collect them at just how heavy they were.
For anyone considering stainless exhausts, I would check the weight against the originals first!