Personally if i were buying as Z8 it would be with a 250 pro XS on it. In a nutshell when it comes to horsepower you will never regret having more, ever. It has nothing to do with top speed either, all of the motors will move it plenty fast enough. Think of when you have the boat loaded to the max with two guys, a bunch of gear, full livewell and fuel. The smaller motor will struggle getting that load going, now throw some really rough water into the mix and you will be wishing you has opted for more power when you are spearing waves because you cant get on top of them.
I own a a Z7 with a 175 Pro XS, i had options of a 150, 175 Pro XS or a 200hp. I knew i would not have been happy with the 150 so i scratched it off my list instantly. It came down to the 175 Pro XS which makes darn close to 200HP or the 200 opti which makes a little more then 200HP. I went with the 175 because of fuel economy and i wanted the extra goodies the pro XS comes with. The boat is plenty fast with the 175 and generally runs great. Do i wish i got the 200? Yep, there are times i do. Those times are mainly when i have an extra guy or two and a full tank of gas. If i had a do over i think i would opt for the 200 just for the extra torque and ponies.
basstrackerma, as far as Pro XS vs non Pro XS goes. I would get the XS all the way. Maint wise there is no difference between the two. The big difference is the solid motor mounts, low water pickup, carbon fiber reeds and upgraded fuel injection. The Pro XS is said to be better on fuel vs the non pro XS motor and the carbon fiber reeds are a big plus in my opinion. The regular ones come with stainless steel reeds and if you have ever had a motor crack a reed and injest it you will know why you want carbon fiber. With stainless the motor is toast at worst and at best needs a new piston and a hone job, with carbon fiber its an easy fix.