Hi.
I have a 2007 Interceptor. I can tell you this with accuracy about the use of 10W-30. Between 2006 and 2007, Honda changed the oil "recommendation" from 10W-40 to 10W-30 in the VFR800. They made absolutely NO changes to the engine....just changed the viscosity recommendation. I got curious about this and talked to a friend who works in the motorcycle division of Honda. He confirmed NO changes to the engine. i.e. ALL that changed was the print in the manual! The real reason they made the change was for better emissions....NOT because of any engine issue.
The 2007 Owner's Manual shows that 10W-40, 20W-40 and 20W-50 were all APPROVED for use in the VFR800. Note that MANY bike manufacturers recommend 10W-30 for use ONLY BELOW 80 deg. F. ! The VFR1200 is a totally new breed of cat, so am sure they did all new product testing with the recommended
10W-30 so it is extremely unlikely it would be inadequate in that bike. THAT SAID, however, I sure would have some oil analysis done on that oil a time or two early on to see if it was shearing badly. I also would use synthetic in that application.....lastly, I probably would end up using 10W-40
synthetic in an engine that puts out that kind of HP! I would bet a LOT of money that 10W-40 is fine and/or better than a 10W-30 in that bike.......Just my two cents......
FYI: I have two Honda cars that spec. the 5W-20 and I have run mostly, 10W-30 in them. All that I can see is happening to those cars is that the engines are going last FOREVER based on oil analysis and that is confirmed with the way they are retaining performance at high mileages. I HIGHLY doubt that engine is going to explode in a ball of black oil mist, with parts, valves and little gear wheels flying every where if you ran 10W-40 bike oil in it. Logic: I can promise you, that 10W-30 on a 26 deg. F. morning in Minneapolis, MN (you had to ride your bike to work on this cold morning because your truck broke down and your wife has the car!!) is going to be a LOT more viscous in the bike than if you started it with 10W-40 in it, under the same situation in Phoenix, AZ in June when it is 96 F !! Both oils will work FINE in either situation ....again.....this is my OPINION.....
Best Regards.......