Up to about 10% there's not much in it on the S40 vs a trad roadbike (Al frame), but once you get a bit more than that, or it's wet and slippery, the FWD characteristic of the S40 becomes unuseful as you start to get wheelspin and slippage. You can reduce that with lowering tyre pressure, but there's not a lot of room for fatter, grippier tyres than 28mm. In the dry I've negotiated 14% or so, with light touring load, but a damp hairpin almost cost me enough momentum to be off and walking.