What size is your other kite?
Do you want overlap b/n your new kite and the existing one, or just something that is light wind dedicated?
In terms of the Best Waroo 17, it's my opinion that is overkill and that the 15 would work at your size.
Once it picks up, you will be able to hold onto a 15 longer and not get blown off the water as fast as on the 17m, as well.

Just something to think about with these light wind kites - There is a point where more kite in the sky is just more drag and slower, and not worth it, imo, unless you weight 220 or something. It's not like you are going to be jumping in 10 knots on a 17m and not jumping on a 15m.
You will "just be riding" on both kites in 10 knots.
Once it hits 13-15, the 15m is not outclassed by the 17m, probably the opposite actually, cuz most 16/17m kites are pretty slow.

Also, if it picks up on you to lets say high teens, you will almost definitely be having a better time on something than a 16/17m, unless you are a glutton for holding down a big, pull pig.

That's my take, anyway. I don't even have a kite bigger than a 12.5 these days and I weigh 165.

If that wasn't the case, I would need something bigger than a 12.5.

Can you demo a 17m kite (of any kind) and then demo a 14/15 and see if what I say is true for you?
That might help you out.

Of those choices you listed, I would just flip a coin or go with what "feels right". I have ridden all of them and they all pull like a truck in light winds and will get the job done. None of them smokes the other, imo.
Sounds like you have a light wind board already. That's what is going is going to be the more important factor in the light stuff.