I'm not against anyone selling horses. Riders change and evolve, horses don't turn out like we thought, whatever. There's no reason to think that you should be stuck with one horse forever, especially if you want to advance as a rider. What I AM against though, is discarding a horse for a newer, brighter toy...if a friesian is your life long dream, that's fine. But make sure its not an impulsive decision.
If you want to sell Denny, that's absolutely fine. But make sure that he has a place to go. In this market, horses are being dumped all the time. Fort Macleod is loaded with decent horses who were cast out because they werent fast enough, good enough, or just overlooked.
So the point of my rambling lecture is this; if you don't think Denny is what you want, and are convinced that you want a Friesian (it is a very good time to buy) then sell him. But make sure that he actually has a place to go. Otherwise, all that hard work you put into him will be for nothing, because he WILL go to slaughter.