I don't have the same boat or the same engine, but the general idea is exactly the same. I have a 15-1/4x17 on my Yamaha and I can get to the top of the RPM range (5,500) at a touch over 40MPH. Is 6,000 the top of your engine's RPM range? For now, I'll assume yes. So, going on that, it sounds like you're propped pretty well and I'm not sure I'd start messing with lower pitched props since you'll over rev your motor at the top end if you're not careful. You'll also end up running a higher RPM at cruise. Tweaking your current prop could help some, but it's only going to be very minor.
-- Make sure your engine is trimming all the way down (physically check this)
MOST importantly:
-- Does your boat have trim tabs? Use those. If not, put tabs on - they will make a HUGE difference in both your hole shot and planing speed.