When playing with higher point values with SM against Orcs, I suggest the balance between heavy weaponary and high fire rate weapons. First things, first, try to destroy his transports. Orcs are menacing enough, you don't want them to go speeding up on the battle field and actually do a 21"-26" assault. (Orcs can do it, there has been a topic before, open-topped vehicle, 12" move, 2" disembark, 1"-6" run move, 6" assault). You want them to walk. So bring along some lascannons and missile launchers, it's also very good to take down the armoured nobz, for the rest heavy bolters, assault cannons, autocannons, bolters. These can take down the ork mobz when they come towards you. You will always be outnumbered, no matter what, space marnies don't tend to be with a lot. Just hope your 2+/3+ save will be the hero when they assault and perhaps defensive grenades so you can hit them first.