I wouldn't change your fiber optic sights until after you have done some shooting with them. I shot well with them on targets, but did install a rear Williams peep sight after finding that my aging eyes don't work as well as they once did. The front FO sight was easy to see, but it blocked most of the deer that I shot at 204 yards, so I later changed to a Globe sight. I used that set-up for a CO hunt last year, and found that I could aim more precisely, but did lose some of my low light aiming time. I have another MZL hunt this year, and will make a decision about which front sight to use after a lot more shooting in varying light conditions.
By using a chronograph, I found that the gain in velocity is minimal after 120 grains of powder, it was mostly more smoke and recoil, with some loss in accuracy. That is something that you have to discover for yourself. I've shot a couple deer with the Powerbelt bullets in MN, and tho they did the job, I can't say that I was entirely happy with them; hence my switch to Hornady sabots. Whatever you do, when you change any component, the entire equation may change and you have to spend time on the range. I also found that there is a big difference shooting out of a fouled bore, so after my final test shot, I clean it well, then fire a fouling shot before going on the hunt. Good luck and happy hunting.