The point about wind protection is well taken, but as Darris commented to me several years ago "I have wished a thousand times that I (he Darris) had built the XB-2003 and Grand Sport on the 21' hull". As the owner of a 1989 XTB that I bought new in 1991, I know without a doubt the 21' hull is much more suitable for my location now due to the increased cruiser traffic on Fort Loudoun and Watts Bar. After going from an old 16" Bomber with an 80hp Mercury to the 21 XTB, I thought I had bought a battleship--now the 21' XTB seems like the provertial bathtub out there on the weekends. And, of course in the last few years the weight factor of the larger Optimax and 4-stroke engines make the 21' a hindsight right choice.
If the cruiser traffic and big water were/are not issues, then the 20' hull of the XB-2003 and Grand Sport was/is a good choice. A 150-175 hp Mercury/Mariner in stock setup will push the 20' hull 2-3+ mph faster than the 21 XTB and probably give a bit better fuel mileage. And cost--in 1991 when I bought my 21 XTB, Mueche Marine in Kingston, Tennessee had a beautiful new white and red Grand Sport and trailer at the closeout price of $10,400. Add say $8,000-10,000 for a new 150-175 Mercury and some rigging and you had a sweet, good wind protection, mid 70s mph Allison.
In summation, nearly all products and equipment on the market have design choices to consider--on Fort Loudoun on the summer weekends these days when all the ever larger crusiers are out, I'll trade the 21' hull for the 20' and its much better wind protection every time.