Hi Andrew and welcome.
I and a number of others have converted the gearing from the factory 15-41 to a much nicer on the freeway 15-37. This lowers your cruising rpm by almost exactly 10%. You also gain the added advantage of correcting the inaccuracy of the speedo in the bargain.
It slowed my 1/4mile times about 4 tenths and 4 mph but the CB-1 will never be a stormer on the strip anyway. Top speed is virtually unaffected because Honda factory gearing was such that you ran out of revs (hit the rev limiter) about the same as the top speed is due to aero drag no matter what the gearing. In other words my bike still hits the same speed but it runs out of power just below redline instead of 1000rpm above redline bouncing off the rev limiter.
I don't think that the change would really have a significant effect on the bikes use as a track bike because your don't do standing starts where the gearing hurts the dragstrip performance and you would likely never use the sixth gear as top speed in 5th is the same anyway and unless the straight was extremely long or downhill there would be no benefit in changing up.
As for the Kerker, you could look around for another slip-on, find an oem exhaust which would hurt your performance somwhat or I think my choice would be to repack the Kerker as it is likely blown out. Aftermarket systems for this bike are not easily available and are approaching half the price of a really nice complete bike.
Enjoy your bike, keep us posted and
