Davis Yost designed several small solo trippers; the Curtis Vagabond 14.75' in ~ '82, the Swift Loon 14.5' ~'92, the Placid RapidFire 15' in 2005 and the Swift Keewaydin 14' in 2014. All are 27.5-28" wide max beam and are tumblehomed. The Kestrel is splashed from a modified Vagabond. Loon and Vagabond are NLS.
The Peregrine is splashed from a modified Curtis Nomad, 15'4" '85, Yost's fourth large Solo tripper. It was followed by Swift's Heron 15' ~92, Bell's Merlin II 15' in ~'96, Swifts Keewaydin 15 in 2011-12 and NorthStar's 15'5" Northwind Solo. All are 28.5-30" wide, the later wider as society has "supersized" itself. Heron and Merlin are NLS.
The larger boats have higher potential speed because they are longer but more drag/resistance for the same reason. Their width increases stability but compromises the paddler's ability to employ a vertical paddleshaft.
Your client probably won't notice a significance in immediate tests unless he/she is small in stature. If dedicated to the double blade, the Placid RF and Swift 14 and Kee 15 are available so rigged with low seats.
For kneeling paddlers, Kestrel, RapidFire and Kee 14 are available with kneeling seats among the smaller hulls, Nomad, Peregrine, Kee 15 and NorthWind Solo are available so trimmed among the larger hulls.
Best choice? how large is the paddler, how much power do they use and what is the preferred stance in the boat.