In my experience, an 066/395-class saw becomes necessary when you're routinely burying a 32" bar in hardwood. If you have any need to regularly run a bar this size or larger, you need a bigger saw. A 100cc+ saw (3120, 084, 088/880) is helpful when pulling a LONG bar is required, say 40"+. A saw of the 066/395 size or larger can be helpful if you're cutting up larger diameter firewood, since that's a lot more cutting - every 16-20" - compared to logging where you're processing stuff into 8' or longer lengths, making fewer cuts.
I've owned those big saws before and ended up selling them off. They just didn't make sense for the sort of cutting I usually do. There is very little that I cannot get done with a Dolmar 7900, Husqvarna 272, or Stihl 044, and the sawsare a lot lighter and more nimble. And with bore cutting and wedges, you can still handle felling the occasional really large tree just fine. I own no 60cc-class saws as they don't fit into my line up; if I don't need the 70-80cc machines, the work gets done with a lively 50cc with 16" of 3/8" chain.
There is a tendency on this site, and elsewhere on the interwebs, to fall into the belief that big trees require big powerheads with long bars. This is not always true. Sure, big powerheads and long bars are nifty and give you bragging rights in certain circles, but honestly, if you think back over the course of a year, how many huge trees did you drop that required this sort of kit? How many times did you really *need* a bar >28"? Odds are not that often.