I personally think that 2" will make a difference in stability. You imagine 5cm more on your surfboard? Thats alot IMO. 29" would be the absolute less Id go but thats because Im still a kook. Flat water paddling is easy but when you get into the waves its a totally different sport! Plus putting your kids on the nose of the board you also need more stability. My Starboard 11'2 is 190L in volume! And thats nothing compared to the Naish 11'6 which I think is about the 230L?
Um mast track was important for me firstly because I windsurf and didnt want to spend big bucks on just a paddle board. Also when the kids want to learn windsurfing I can put a kids rig on it. Obviously its not gonna be a hardcore DTL wave board. Just ask Miller. He had his Naish out in some big waves.
For me its an option to put my 5.7m on it and flog around in 10-15 knots.
Its versatility is cool.
For instance I wanted to go for a paddle late this arvo around 7pm. I drove between Trigg and Hillarys looking for a wave but the wind was also abit too much for my liking. Southerly about 5-10 knots. Although I was dying for a wave I just had to get out and paddle so I just went to the marina and paddled around for an hour on pure glass water. Magic and relaxing. Plus a good workout

Hope my rambling helped make your decision easier