Good deal on your swap out. It doesn't surprise me that the NX box would provide better low end grunt through the timing curve; considering the intended different uses of the bikes involved.

I've wondered too how much power in what part of the band could be tricked out of the Savage by tinkering with the CD box. I got to searching around the 'net and couldn't find anything on anyone tinkering with the Savage CDI specifically, but I did find some info on reverse engineering of the box on some other bikes (can't even remember what at the moment).  Anyways... I did find claims of considerable power gains by tweaking the actual components inside the CDI box.

However, as owner of both late and early model (87 and 2-99s) Savages, I couldn't say that the 87 exhibits any power advantage in any way over the later model bikes. I think the Savage was strictly engineered to fit the HP limit rating for novice riders in Europe, and hasn't changed any more than it would take to meet EPA or other enviro standards. I suspect that most of that was done by just starving the poor engine with the small jets and lean idle mix. Having said that, I do know that besides using restriction in intake and exhaust to intentionally reduce power, Suzuki and other's have also purposely de-tuned their bikes through limitations in the electronics/timing curves.

So... I seriously doubt that a swap to an early CDI box is worth the change; but the question remains: Is there some other CDI box substitute that would be an easy fit and power boost to the Savage; or would it be possible and worth the effort to spend time and/or money trying to reverse engineer a Savage CDI box?

Ahh... I just found another site that includes the results of experiments with the CDI of a DR800!  It seems there is considerable information already existing, and it might be possible for someone determined enough to make a worthwhile effort on the Savage CDI...

Although, as a life-long electronics hobbyist, it is the sort of thing that would be of interest to me, I'm so buried in motorcycle, guitar and amplifier projects right now, I'd never make a promise as to when I might take on a project of this depth.