Just curious, but why do you 5w40 instead of 10w40? Availability? Better cold start performance? The brief search that I did, I don't see a reason why it would really matter. Granted most of this stuff is hearsay, it sounded like it was from knowledgeable people. The difference between the two oils is simply the viscosity at a certain temperature, but the viscosity is the same once the engine is warm. Basically the 5w is slightly thinner than the 10w at start up. The only thing I seen being a negative is that this is caused by additives into the oil that break down sooner....?? So someone said.
Another oil thread huh.
Through the life of your bike it really does not matter, most Busas will not see 100,000 miles or even close.
In a normal motor, wear only happens when the oil film breaks down. In a reasonably stock Busa, under normal operating conditions, the oil film only breaks down after the motor has not turned for a while and then for a short period after start-up while the oil pump moves oil to all the critical lubrication areas.
So, in short, most of your wear happens during cold start and a 5W40 is a bit thinner when cold, so the oil pump gets it where it needs to be a little faster.
Some tests done some time ago, you can google the data, shows that on a Honda Blackbird, there was 2-3hp gain using a 5W40 synthetic, compared to a 10W40.
A good 5W40 is more expensive to make, as the viscosity polymers have to stretch a little further and need better shear resistance to keep the oil in grade. The base needs to be a bit better as well.
In the end we are splitting hairs here, really not that important. I do an oil analysis with every change, just for fun and because I enjoy my bike. The main advantage with that is showing me how the oil holds up.
When we spend money on oil, we do it in good faith believing that it does everything the marketing dude said it would do and every marketeer says his product is the best. An analysis is a good reality check.
The shinko's that smoke or the regulars? 
