Adam, the question to ask yourself is, "Why do I want to do this?"
CATERHAM said it well. There's just no advantage to a heavier oil than specified in most cases. The only reason to use it would be in super hot climates and/or hard continuous use (in both cases we are talking regular operating oil temps in excess of 212F) or in an engine that has viscosity loss problems due to fuel dilution or shearing. Do you fit in either of those two scenarios? If you did, most likely a 30 grade oil would be all you need anyway.
As to the VTEC, the potential is there for the heavier oil (it's two grades above what's spec'ed) to disrupt operation in some way. I'm less worried about that than I might have been due to some experimentation with my own Ford's VVT system with a one grade increase in viscosity. I datalogged my EFI system and couldn't see any changes going from a 5W20 to a 10W30. We may be talking about apples and oranges here comparing Ford to Honda, though. FYI, my reason for the change was not that I felt theengineneeded the heavier oil, it had more to do with my wallet and my sanity. I was looking for one oil that would work in all of my small farm fleet and 10W30 HDEO will fit the bill. I'm willing to sacrifice a little MPG towards that goal.
We keep hearing, "Oh they only went to the 20 grades for CAFE." Ok, so what if they did? It hasn't hurt anything. Engines are still going past 200K mile. There isn't a rash of failures over and above the normal rate. What's so wrong with better MPG... even if it's not a huge increase. More to the point, what's the demonstrated advantage of going two grades heavier that makes it worth the loss of fuel economy? Demonstrate a need!
Adam, nobody that's clued in will argue against a choice to use a heavier oil when there is a demonstrated need. Like J.B. Books said, "when you needs six, load six." You can use what oil you want, of course, but think of your own bests interests here.
Remember: "As thin as possible, as thick as necessary."
