Ask Stoicbloke, he was on Siracs in the Lakes - I can confirm he never had any trouble keeping the pace.
Here's another one on Siracs (I think he was anyway) - Chekamus
If you're in the mud then the dual sport tyres just don't cut it, but for most trail stuff, up here in the lakes anyway, they are fine. The manual suggest a slight drop in pressure, but these guys had just spent all morning on the motorways and then straight into some off-road stuff, so I'm not so sure....