Thanks for the input, guys. Here's some actual experiences with those designs.
The Nemesis was just a wild idea that I had, but it fails rather miserably at its task. Energy weapons just don't cut it in a purely supportive role, not even in Polar setting. An added problem (with my team setup anyway, having many large titans) is that many of the larger titans carry a shield, cutting very deeply into the reliability department. And even with its superb heat reduction rate AND Polar climate the thing overheats all the time unless you use like 3 out of 4 PGs only. Ergo, it would actually be an improvement to toss out one of the PGs, at least it'd let you trade that Millenia for something more useful in some places. As I noticed, it doesn't really make THAT much of a difference if your heat reduction rate is -6.1C/sec instead of "just" -5.7C/sec, especially if it means that you'll be tossing out one third of your armor to get there. It just MIGHT be worth it in Hell setting, but that'd also rule out the use of PGs due to their abysmally low damage/heat ratio.
The 4 LLs in a Lightbolt work in Polar setting, though, overheating very little when standing still. Keep in mind that a LL has a much better damage/heat ratio than PG. If and when you need to do an active scan, the added heat will be pretty much gone once you're done with it. But just as with the Nemesis, this design works better in smaller teams as the opponents won't have that many Heavies & Assaults with shields installed.
When designing the Ice Demon I already knew that there might be some problems ahead if I leave shields/ECM home. And boy, was I right! Unless you're playing rookie/green AI opponents, you'll be having called shots (esp. energy weapons) coming your way much more than any imaginable armor could withstand. Plus, being encumbered by such a large engine and having so many things reducing your chances to use the full power output to recharge weapons I found the power management too arduous to bear. Also, since the range of those CLGs is rather limited, I found it frustrating to just act like a sitting duck before I could return fire. And, by the laws of Murphy, once you finally get in range, the first couple of titans you'll encounter WILL have shields, and you're scr3wed.
As a matter of fact, the CLG has a rather interesting problem with it - it's plain impossible to max out the heat reg with it due to power output problems, since you can't just expect to stand still when you have such a lowsy range in your weapons. It works better to ambush your enemies with it, though, and I'd imagine it being a lot more usefull in Hell settings, where even the best heat regs have trouble coping with all that extra heat.
Jukka Mikkonen a.k.a Sir Rechet