i heartily recomend that you twin-link any guns on your shooty 'fexes... sure it means they won't be so good in assault, but with only a max BS3, those re-rolls will more than pay off with the casulties you'll inflict! (and the tanks that will spend the whole game stuned/shaken!)
plus, by keeping 'fexes to a single role you'll also help keep them cheaper than if you try to tool them for both shooting & assault... (just think of all the extra gribblies you'll be able to get too!

)
cheers!