My guess is that a 4 % change in gearing is more noticeable by the timing of gear changes for any given road speed, than seat of the pants accel in most modes of normal operation.
Maybe some sense of softened power, but my guess is that would be most noticeable in just the top 3 gears.
What remains is this, a 17/44 setup nets the following road speeds @ WOT @ 9400 RPM (200+ revs of nice stable flattish over rev power past peak power):
65 MPH in 1st Gear
88 MPH in 2nd Gear
I think you need to examine what gear/gears you are using for accel and merging.
With a 17/44 you should be able to accel so hard that your problem becomes having to brake to slow down to match traffic.
In 2nd gear.
One area that was pretty clear was coming out of a stop light. Before, I was able to lift the front wheel without much trouble, now I'd have to work at it if I'm able to. When someone says "4%" it makes it seem like I should barely tell the difference, yet I noticed it right away. It wasn't like I did several changes at one time, I only changed the chain/sprockets at that time so nothing else changed.
It does seems strange on the surface that 4% would even be noticeable, but I also didn't confirm that the sprockets were original, so maybe it wasn't a 16 to start with, but that would make something like an 8% change (IIRC) and that seems more reasonable.
I really don't think there's something wrong with the bike in terms of power output, but at the same time, I don't know how to compare it.
It could be one of those "running on 12 year old tires" things or what happened with my forks about a year ago when the fluid was slush and it made a big difference.
I've never done the valve adjustment or the starter sync thing, so maybe that has and effect, but IDK.
I guess I really should tear into it a bit more, I don't like covering up one problem by buying a solution that hides it, but at the same time, the PCIII seems to be a nice upgrade from what others say about the low end jerky problem.
It's not just this bike, most bikes you have to give them some gas and feather the clutch to get them going, the 919 is known for lower end torque, so a strong pull low would make it jerky.
I do have the carb sync tool and probably should check the valves as I'm at 40,000 + and don't know that they've ever been done.
Given that the PCIII is $200, seems like a pretty good investment, I'd just have to find a way to ship it somewhere else or have someone else buy it for me and ship it to me.