They do make an efficiency Kit for the new style Shockers, not sure what's in it, but it exists!!!!
Try em both, as you might find a certain set-up more of a preference. I found the new style Shocker wicked easy to shoot fast on my off-hand due to it's size and light weight. Any well set-up gun is going to be good, even if the anti-SP brigade will try and tell you otherwise.
Although I'd always be inclined to work out who my nearest supplier is, establish some rapport with them, and just give them the gun back to service, make go boom (hence I've never had a bad Impulse, ever).