I've had a few britts, including one that was my favorite "once in a lifetime" dog.
They can be pretty energetic. I've owned a GSP, and with that sample of one, I would not agree that britts are less wound up. Anecdotal, though.
There are three big differences I think you will see. First, britts (and other spaniels I've owned) are very much companion dogs. They want to be with you more so than other breeds.
The second difference is the coat. That long hair is a maintenance issue, plain and simple. You may or may not spend a hour or two digging cockle burrs out after many hunts.
Third, they are very intelligent, to the point of being devious. Not a bad thing, and quite often its amusing.
Aside from that, I think any other differences come down to the individual breeding rather than the breed. Britts are one of the "big four" breeds you see in field trials like NSTRA and AKC, the other three breeds being English Pointers and Setters and GSPs. That should tell you in terms of hunting ability, its a wash from breed to breed. Those four seem to comprise 80-90% of the winning field trial dogs.
They're great dogs. I'll own another one someday. They may or may not like water. Mine didn't. So if you still want to do a little light waterfowling (they cannot handle a real cold swim) they may not be your thing.
I've been pretty impressed with some wirehairs I've been around. From what you describe, they might be a great breed for you too. That will probably be my next pointing dog.