Hi Matt,
The GO offers a higher level of performance (better ride/speed/control/response) in the planing (top) half of the RIO's performance range, thanks mainly to a more planing oriented design and lighter overall weight of the GO(s).
For more versatile overall range, and more performance in marginal (sub planing) conditions, the daggerboard option on the RIO presents the better option, albeit at the expense of some reduction in planing range performance (which is where the GO shines over the RIO).
Apologies if the answer seems as boring as the question
- but you get the idea !
Cheers ~ Ian