it might be that you are paying attention to the wrong things..
thermal load should have gone from .2 to .6 or similar, the 200 or 245 is % increase from an unmodded to modded mc
look in your outfitting to see the actual values, and if you can, put an image of it in here and then maybe someone can explain for you.
as for use of overcharged or efficient, each to his own, overcharged is what I use along with beams, heat efficiency is easy to control by either the type of beams or how I use the weapons in combination and time used for each...all things a person either learns or doesn't.
IMO MC's thermal is such a minor concern certainly not a concern in my case...when my ships get too hot from the beams even when using thermal experimentals, I simply either stop firing, or fire MC's only till it cools. And I tend to use OC MC's with incendiary and with corrosive.
My vette for example is 1x 3C OC MC with incendiary, 2x 2f OC MC with incendiary, 2x 1D HiCap Rails with SP, 2 4A beams, 1=efficient with thermal conduit, 1=LR with thermal conduit
most of my ships have variations of this, with some exceptions where I use short range beams for maximum heat effect and thermal conduit
The jist of it all though, is numbers aside, experiment and see how it works for you and go with what you like best..