Skill leveling an SR assault in order to accomplish what you want to do in the near future is perfectly fine. How high should you go? Well, some would say 20, others would say lower. What it comes down to is this: you must understand that at some point in the future, an SR will get replaced by an SSR. How far off into the future that will be varies. So you're internally making guesstimates of how much you'll actually utilize this weapon until it's replacement time as well as weighing the value of the resources needed (both the fodder weapons themselves as well as your time).