You can drastically increase your rate of fire, both as Jason (in top-down only) and Sophia, by assigning your blaster to a shortcut. By alternating between the regular fire button and the shortcut, you can basically turbo through the game. Remember to mind the sprite limit!

As to whether this method is better than using a shortcut for an alternate weapon is currently unknown and may even depend on the run. In an Any%, this method is effective because you have so few subweapons and almost none of them are useful enough to keep on a shortcut. In my own 100% runs however, Impact Wave, Burn Spark, Grenades and S.A. Attacker are used often. I don't know that the time saved with Rapid Fire wouldn't be lost elsewhere. Try this technique out for yourself and post your thoughts in the forums.