I run a PWK 28, I had a hell of a time getting it jetted. Thats the main disgruntlement about the Keihins, on here, its hard to find good jetting numbers cause most of the people run stock carbs, or bigger 30-36mm carbs.
For a stockish blaster, I dont know how much power is to be had by moving to a PWK 28. I honestly dont think Id even worry about it if you have a stock carb already. I dont know if Id even worry about upgrading that carb till your engine is ported or stroked (ported AND stroke hehe), and you have more breathing mods than you currently have.
Im actually tempted to pick up a stock carb and toss it on and see what it does, cause its stupid easy to get jetted properly with the myriad of info on this site. You can get jetting numbers from TONS of people on here.
With the 28, theres just a small handful of us.