Here's my take on it. 2 more DHS (really just 3% efficiency, but also faster cooling) and 6.3 kph faster. I was using an AC/10 in the arm with a 300 XL, but found I rarely used the AC/10 due to my playstyle, and so that was 16 tons that could go to speed and heat sinks.
Okay, I really like this. The combination of being able to snipe from rooftops or with JJs means my best weapons are mounted on the shoulder. If I mounted a weapon on the arm it would barely ever see any use through my peek-a-boo tactics. This build lets me get a bunch of DHS instead and make it so I can keep up some constant damage. It's also useful for shooting over the line of friendlies I'm using as mechshields. This thing is a beast. I use it mainly as a peekaboo sniper, whether I'm on a roof, a hill, or just poptarting from behind cover.
Never a bad play... Dual Gauss is nice, but, much harder to time. This allows you the same recycle rate, the same projectile speed, the same damage - without the nagging problem of missing targets because your Gauss and PPCs were out of sync... Not a bad build at all!