Milling your jugs to obtain a zero deck will give you about 10.5:1. That's about the limit for pump gas. A zero deck will maximize efficiency and will allow a slightly higher compression ratio before detonation (compared to milling the heads to achieve the same compression). These bikes come from the factory with a horrible negative deck height.
If you want more compression than that you will have to mill the heads but I don't recommend this unless you're going all out (race only). The difference in power between 10.5 and 11.5 is minimal, but would require race fuel to be safe, or a retarded timing table which would kill power.
Looking at your avatar it appears you have the V&H 2-1 pipes. My concern here is that your primary pipe size is (I believe) 1.75". This pipe was designed for the smaller HD motors, not big inch S&S. You need a 2" primary exhaust to maximize power. See the link in my sig to see the 2-1 pipes I'm using from RBRacing. They also make what they call a "124 Challenge" pipe utilizing a merge collector. This is an all out race pipe without a muffler. Some use it on the street though with good results. But both of these pipes make very good power compared to most others. And I'm talking good average power, not just a good peak number. Average power is more important than max peak for best acceleration. The reason I bring up exhaust is that if you're going to spend big bucks on heads you don't want that power choking in the exhaust.
If it were me I'd maximize the efficiency of your existing combo before I went and spent major money on new heads.
