Well, well well-- I went and got a new router (Linksys BFSR 41 v2) to test drive, but much as I hoped to see an improvement--couldn't. As a true Ultrapeer, the number of Current Hosts fluctuated in the low 50's.

Since hiding connection view, the number seemed to fluctuate in the high 50's, going up to 64 for a moment or two, but also down to the high forties. Thanks for the tip . . . I'll take the router back and save a few bucks.

So, can't repeat et voilà's stability as an ultrapeer behind a router: it's not the router nor the DNS lookups. Plenty of bandwidth, processor power. Looks like life as a leaf is not leeching since uploads actually are better, searches are fine, and downloads work quite well. I can always connect directly when the family doesn't need the net and run as an UP then.

I'm out of ideas what else to try since Windows is not an option