4cyl vs. 6cyl

I have sort of an "open" question. I currently have an older (1982) 15.5' trihull with 70HP outboard. I am looking into buying a new boat and would like some of your opinions on 4 cyl vs. 6 cyl. I'm looking for a bowrider 17' to 19' length. I have been noticing that most of the boats in this size range have the 4cyl engines, but some (most) offer a 6 cyl option. It would be used mostly in fresh water lakes for pleasure/ fishing/ tubing/ some watersking and wakeboarding. I have two boys who think "the faster, the better". Is the 6 cyl option generally worth the extra money? Would the 4 cyl generally be underpowered? I have heard both good and bad regarding both engines. Any comments would be appreciated.