It seems that most people opt to fit the US spec Vance & Hines silencers and then remove the baffle (because with the baffle fitted they're quieter than the standard silencers and they don't sound as nice as the standard silencers). I had a demo ride on a Street Twin fitted with the US spec V&H silencers (baffles removed) about 2.5 years ago, and I thought they sounded great but were a bit louder than I would like. I've had much louder bikes in the past but I now prefer my bikes to be quieter when crusing at ~60mph. So I've just treated myself and bought a pair of the EU spec silencers, and I thought I'd add my comments about them.
Like most people, I like the standard silencers, but I thought it would be nice to have silencers that are a fraction louder and deeper sounding. I've just fitted the E mark V&H (both these and the standard silencers are marked with the E-9 marking) and was fortunate that the roads dried out so I went for a short ride (~19 miles). Starting the bike in my garage and initially during the ride, I thought that there wasn't much difference compared with the standard silencers. Eventually I thought that they may be a little bit louder and deeper sounding under acceleration, but it's only a small difference - so small that it's not easy to tell. At 60mph cruising they might be a faction louder, but again it's only a very small difference. So the good news is that I like how it sounds, but it's a lot of money for a very small difference (I was able to buy them for £479, a 25% reduction compared with the £640 RRP - although I've just seen some for sale for £460)!
It's perhaps not surprising that there's not much difference as they're very similar silencers (I believe they're both made by Vance & Hines). Both the standard and V&H silencers are straight through. The V&H have a short (~1cm) long restrictor ring that reduces the bore to about 18mm diameter (down from an exhaust pipe diameter of around 40mm). In the standard silencers that 'ring' is about 10cm (4 inches) long, and is perhaps the main reason for the silencers being longer (I measured the V&H as about 7cms or 2.75 inches shorter). I think it's the same diameter restriction, although it might be about 1mm narrower. The standard silencers have an exit diameter of around 31 mm (so another restriction there) compared with the V&H around 40 - 42mm. Up to the restrictor ring the inner walls are solid metal, and it's perforated after the restrictor and presumably packed with wadding to the outer skin. So there's not a lot of difference between them. I guess the US spec V&H without the baffle doesn't have the restrictor ring but is otherwise the same (although I think the exit of EU spec versions looks slightly better because it doesn't have the ridge for the baffle and C-clip).
I weighed the silencers while I was fitting the new ones (being divorced I can use my kitchen scales without fear of being moaned at by a wife!
). The old silencers weighed about 2.72kg right and 2.82kg left. The V&H weight about 1.75kg right and 1.95kg left. So that's about a third less weight, and a total saving of 1.84kg (4 lbs) - not a great deal of difference really (less than 1% of the bike's weight). I'll have to wait until the spring/summer weather to ride far enough to be able to figure out if it makes any difference to the fuel consumption - I would guess it won't make much, if any, difference.
So to conclude, if you're short of cash I would not recommend buying the EU spec V&H silencers, as they're not much different from the standard silencers. If you can spare the cash and want to treat yourself, then they do look a bit nicer, and possibly sound a little better, so it is a small improvement, albeit an expensive one!