I am surprised no one posted an LB20X build. Like the popular AC20 build this uses a 300 engine (STD of course), so the speed is pretty good. LB20 does not have the WHAM! effect of the AC20, but it is much easier to hit with (significantly faster projectiles) and will mess up opened compenents pretty bad (or good, depending on whether you are in front or behind the cannon...). Plus, LFE300 engines are in high demand for numerous other mechs, and I had this STD300 that way stashed away in the garage. Fun mech.
This with SPLs and a Rocket Launcher and a STD280ish is pretty fun in Solaris 7, although it can’t win against everything in its division with ease.