Mikuni's are great carbs, but if all you have done to the bike is pipes it's probably overkill, you should be able to rejet the stock CV & wake it up a bit. The Mikuni is great if you're going to do cams & ported heads & such, but it will work great with just pipes if you find somebody to tune it right. It doesn't make any difference if it's carb or EFI it still needs someone who knows how to tune it, more guys used to know how to tune carbs, but not sure that's the case anymore, some HD techs hardly know what a carb is these days.LOL
Youre gonna get tons of answers about cams but I think the majority attest to the mikuni for the best carb. Cam selection depends are your riding style and what rpm range you want to feel the power. The search function should get you about all the cam reading a man could ask for.
my brother has a 06 rk carb model, he put air cleaner stage 1 kit, mikuni & rineharts and it ran alot better, but it was more of a better response than better power