When I bought my Magna it had a 16/43 sprocket combination (stock is 16/40). When I changed out the sprockets I went back to stock.. There is a difference.. As Lawrence said, it's a trade off..
Faster start off the line, but not as much speed at red line (shift sooner).. The engine also runs faster when out on the highway.. What's the difference on the highway?? I used to run 55MPH at 4000 RPM.. Now I run about 62 at the same RPM.. Since I do quite a bit of touring, the stock set up is better for me.
If you want to play with the sprockets, I'd start with replacing the 16 tooth sprocket with a 15 tooth. This will give you about the same ratio I had, but the front sprocket is cheaper (smaller) and you probably won't need to replace the chain with a longer one..
IF you really want it to scream and don't want to go out on the highway for long distances, then you could go 15/43..
I have a K&N and I've drilled a 3/8" hole in the rear of each exhaust stack.. This did not require the re-jetting, but I did add a shim to the needle.
SuperTrap has some nice sporty mufflers as well as Jardine and Cobra. Each will require the re-jet.. There is lots of info on the right jets with which pipes, so do some searching on the site...
IF $$$ is absolutely no object, then contact Dave Dodge.. He can probably do some head work, etc.. But, IF you need to go that fast, then you probably either need more than a 750cc or need to go with a sport bike..
Let us know what you decide.