[H4]

Don't think 3" will work any better. You are still limited to the size of the opening in the air box. As long as you go big enough not to reduce the air available to that opening you should be fine. Anything bigger should have no benefit.
I had the same idea about increasing airflow and power as a result. Tried turning the intake on the snorkle to face forward while riding at about 30 mph. Thought it might force air into the box similar to "ram air" or "forced induction" systems. Bike imediately lost power and sputtered. Turned it back around and it immediately went back to great performance. Maybe if you increased the opening in the air box and played mith the jetting you could see a difference with the larger pipe.
Just my .02 as they say.

 

[H4]

I thought there was a post on here somewhere from someone who ran 2 snorkles but had to cover 1 to get the bike to run right.
Cra5h has a good point about the straight runs of pipe. Too many bends or using flex pipe that is not smooth on the inside will reduce smooth airflow. Maybe not enough to make a difference but it will be less than what would be possible with straight runs and smooth bends.
I used 1 1/2 from the airbox to just beyond the front shock then 2" with one 90 elbow and didn't have to make any carb adjustments.

 

[H4]

The snorkle does sound pretty good when your on the throttle. I figured most wouldn't hear it sucking air over the HMF but with my stock exhaust it's really noticable.

 

[H4]

Check the plug.