The RAC-5s are 10 tons so with XL and Endo you can squeeze 2 of em on there. with a 5/8 speed would only carry 4 tons of ammo. with 4/6 speed would carry 7 tons. And I would add the Heavy Gauss to the list of really really wants from later tech. In the sweet spot range of that thing it would be 1 shots on anything up to assaults.
I don't care much for a weapon that you have to spend a turn setting up to use. But the RACs, oh the sweet RACs......