According to the AMA Rule Book, the .3600 cubic inch limit applies to Fast, Slow and Speed Limit. This rule was written when people were using 35's and the 36 gave them some slack. But enough is enough. If the rules gets changed, maybe 26 would be better. Then you could use the abundant 25's with the same amount of slack.
Since Fast and Slow are virtually dead, it's not much of an issue there. Speed Limit, if run by local rules, can be anything the organizer wants it to be. So why buy a new engine that wants to go 100 and try to get it down to 70, 75, or 80? And also risk being disallowed buy somebody who (very correctly) wants to comply with the rules.