RE: Rio, Go or Apollo
You didn't give us much information here.
What is your weight?
What wind conditions do you sail in most often, and what size rigs are you looking at for your new board?
I pretty much agree that the Apollo would not be a real good choice.
It's pretty fragile, and has a limited range of use (up to about 15 knots.
If you liked the GO 155 and weigh < 80 Kg that would be a really good choice.
Adding the centerboard (the Rio) will detract from the early planing and make the board heavier so if you don't rely on a centerboard to stay upwind now, there's very little reason to add one.
If you are heavier than aboout 75 Kg. then the GO 170 might be the better choice.
Hope this helps,