I'll post this here since this is where it's currently being discussed.
I appreciate efforts to answer this question. Certainly the pinion gears, being small, are not designed to be run fast for long periods.
My limited but well thought out perspective is this: Car manuals with donut spares understandably warn against fast speeds and long distances with the spare in use, but even in such an extreme case (tiny tire), 50 mph for a few tens of miles is deemed okay. In the case of the 4runner, the one inch difference is a virtually identical tire size by comparison. Additionally, as near as I can tell, following the same-side 5 tire rotation specified in the 4runner manual puts you at about a quarter-inch wheel size difference near the end of tire life due to tread wear difference (40,000 miles on each passenger side tire, 60,000 driver's side). So, apparently, unlimited driving with a quarter-inch difference is considered nothing.
Taking the two points above into consideration, I would have minimal anxiety driving a 1 inch smaller spare a few tens of miles at 60-65mph. Even so, I'd probably still do a little tire pressure adjustment to minimize the difference.