Feeling like a rather lonely voice out here in forumland, I'm not really in favor of moving the National Rally to early fall or late spring. Without any scientific stats to quote I would hazard the guess that the weather is the most stable and dry in much of the U.S. during July/August. I live in New England and up here before Memorial Day and after Labor Day our weather can be dicey at best. Sometimes we have stunningly gorgeous falls and the easy summer riding weather seems to go on forever and the riding is pure heaven and can go as late as November (no, I'm not one who rides all winter and I store my bike "off-site"). I've also seen our weather turn wet, cold, and inhospitable as if someone flipped a switch during the Labor Day weekend and stay that way until the snow flies. I've also seen New England have intoxicatingly beautiful springs that just sweetly flow into summer. I've also seen New England get snow as late a May 8th and I'm not talking a little dusting of snow - the storm I am recalling we got 6 to 8 inches of the wonderful white stuff and lost a lot of trees and bushes because they were in bloom. I've seen New England have late winter weather go on and on for what seems like forever. This year was a little bit like that.
The last National Rally I went to was in DuQuion, IL, and that year New England basically wasn't having summer - at all. It was sunny and hot at the rally and was just delightful *because* it was sunny and hot (not like the hot this year tho) and that was pretty much all the summer I got that year.
The last trip I took out west to CO on the bike was in mid-September of 2006 and the entire trip was cold. Of the 3 weeks that I was traveling there was only one day that I didn't have the heated grips turned on and all of my cold-weather gear on - and I mean ALL of it because I didn't own electrics at that time. That year was the year of the surprise September snow storm in CO that closed a lot of passes and at that point of the trip I was on a tight schedule to get back east. To find a navigable pass I had to go 2 or 3 hours out of my way south to find one. While the road was passable, the black ice and mid-20's temps were no fun.
So, no, I'm not really in favor of having the National Rally held in May, September, or October. Call me a wimp (I've been called worse) but I don't really savor riding in the cold, the rain, or a cold rain which IMHO you're more likely to have in May, September, and especially October - at least here in the great white north you are. Like most everyone else, I've been there, done that, and still don't enjoy the cold and/or rain on the bike. I'd rather ride in the heat - at least there's always a breeze blowing then.
2004 R115R, before that 1980 R65