I have just purchased an OS .32 for my 31" Pranther V-hull and it is very quick!. Motor was so easy to break- in and tune. I looked at the 0S .21 but have been told that even though it has higher rpms the .32 has more torque and can swing a far bigger prop.
This is not my first boat and I have used other models of motors such as K & B and ASP. OS are not the cheapest but their quality has been proven and they are easy to setup and hold a tune.
But I guess everyone has different opinions, I find that when looking at a specific model of engine before purchasing it helps to talk to people who have actually owned that particular one.