Noosa is a completely different beast than a Nimbus. The Nimbus is a pretty well structured, but still neutral (meaning no physical dual density midsole / medial post) shoe. The Noosa Tri, meanwhile, is in fact a stability shoe, with one of those devices. Given your success with the other two shoes, I’d stay far, far away from the Noosa.
That said, if you find the platform pretty comfortable, you could always try the DS Sky Speed as a race shoe. Same platform, no posting, different (read: non “tri-specific”) upper. Also in the racing category for you would be the HyperSpeed, especially for shorter course events.