Sal,
I am not bug expert, but my experience on the Savage over the last few years has provided a few observations. First, prior to this year, the hatches were multiple and always pretty thick. It was not unordinary to see four or five different mayflies and several different caddis coming off along with the ever present midges, which are an important food source in that stream. Scuds are present, but not in spectacular numbers. This year has been a bit different, but my last trip out there was an exception. Prior to that trip, I saw very few mayflies and caddis and the majority of the bugs were midges with an occasional yellow sally or seasonal bug. The trip that I just took out there was the closest to the past couple of years that I've witnessed, which had me pretty excited!
With regards to your brook trout question, I would say that the water conditions coupled with the forage contribute greatly to growth rate of those brookies. Even at very low flows on the Savage (40 cfs) the water temps remain cool and there is plenty of good feeding habitat (pocket water). The stream does not get hammered with anglers, but it does see its share of pressure, especially on the weekends. Also, there are plenty of forage fish, which I've never really taken advantage of, meaning that I rarely streamer fish the Savage, but I am sure that they are a factor in growth rate. For further information, send me a PM...I would love to fish the Savage with you some day and we can do some field study.