The DDC was once my most beloved mech, but has fallen out of my favour since some time. It's slow, the movement changes are bad for the big boy and for light defense one basically has to rely on a teammate. Nevertheless I kept on trying different variants when in the mood, and this is a result I am quite happy with. Although the Atas remains slow, the weapons mounted grant quite some reach so that the mech can take part in a game's early shootouts at long ranges. One can even mount ER LL at the cost of some heat efficiency to further improve in this department. The AC5s provide very good DPS, and contrary to UAC5s, which I tried on the DDC before as well, they won't leave me alone at random in the middle of a brawl. 3x SRM4 provide quite some punch close up, and combined with the Atlas' staying power and the main weapons they will down most mechs getting too close.
I actually run a STD340 in an Atlas, and it seems to work quite well. I would recommend using that engine to boost your speed. otherwise, it is a good build.
I just built one up very similar to this and then looked at the D-DC section on mechspecs before posting it. I saw yours which is very much like mine. I just have 3xSSRM-2's instead of 3xSRM-4's, with the thought being that it would better for dealing with lights. I also have a ton more of AC5 ammo and some more armor. Otherwise, they're the same.
This is what I run with my DC, which is close to your build: It's my favorite mech and has fluffy dice. I keep a steady stream of AC5 fire on and SRMs with the pulse lasers picking bits off. Usually doing 600dmg +, most I've had is over 1000
