I don’t have Silestone, but I have read that sueded finishes on any countertop surface tend to show grease marks more easily (or maybe it’s just that grease is not as easy to remove with a sueded finish). I would suggest you check out the GardenWeb Kitchens forums at Houzz for more information - there are extensive discussions there on every surface and finish you can imagine (and some that you can’t, LOL).
Having felt sueded finishes in stores I think the surface would be fine for kneading bread - probably better than a polished finish, in fact, because you can get a little better “grip” for shaping.
