X40 are for hard pack, they are good for their purpose. I have had better results on varying terrain with X30 (intermediate) & have found them to be very reliable with good hook up & reasonable wear rate. I ride a good mix of terrain with lot's of rocks thrown in just for the fun of it, they are my "go to" tyre. The X30 front is very predictable & holds on way longer in it's wear life compared to Dunlop Geomax. I have some guys who religiously use X20 (soft) fronts everywhere, they don't have any complaints, although they do mostly ride wet, sloppy crud. The "new" (not so new now) X series Bridgestones are a definite improvement over the "old" 403/404 series.
Cheers,
K