I think the primary difference is the Royal is all hole-puncher, the gauss rifle for the big holes and the ERLL to make a bit smaller holes. IF you do get into the SRM range than it can exploit those holes. I would prefer the LBX variant with CASE refit over the gauss rifle, since 3/5/3 makes it hard to exploit the holes with SRMs. Also, the cluster ammo benefit is nice when you jump and lacks the minimum range of the gauss rifle.
I am really liking the idea of a dual HPPC and LB-10X Crockett/Katana, but the SRMs are definitely going to be shrunk and perhaps better with MMLs. However, after looking at HMP, if you are going that route the LBX has to be shrunk down to a Class 5 to get secondaries. Which is OK since it still critseeks and gives you a long range AA and armor option.
I might revisit this design if my mercs pick it up as salvage against the ComGuards for the 3/5/3 assault lance. It would be interesting grouped with a Highlander, Emperor and jumping Viking.