I have the 75449 on my '02 FLHT and the 75203 on my '05 FXSTD. I have put in some 500 mile days on both and while any seat is a test on a hot 500 mile day, I can't complain about the Mustang seat. They take some "break in", maybe about 500 miles. I have considered sending one of the seats to Mean City Cycles for the removal of about 1/2"-1" of foam and replacing that with gel but have not done that yet. Most of my rides these days are 300-350 miles and there are no issues at all with either seat. However, if I had a long trip planned that required putting in some 500 mile days, I would probably send the seat to MCC for the gel.
The Mustang seats will also change the riding position a bit; some move the pilot a bit forward, some a bit lower, some a bit higher. I would suggest a call to Mustang and asking those questions before ordering although their return policy and customer service is quite good.