The differences are one is plans built & the other a "Kit". The Cozy designer, Nat Puffer, had an agreement with Aerocad principal, Jeff Russell, that Aerocad could produce Cozy IV parts. Russell changed some design details such as glass cloth specs & that ended the approval relationship. The Aerocad made several changes to the fuselage & canopy but is essentially a Kit built, modified Cozy Mark IV.
250 Kts. would be beyond the Vne of the current design limitations. There are 540 powered Cozy IV's that were streached 12" to accommodate the W&B issues. Most recently Scott Carter reported 205Kts cruise in his 540 powered Xtra EZ (see http://www.eaa.org/experimenter/articles/2010-08_extra_ez.asp)
No pressurization needed! Well, O2 vs. the altitude is not the issue here, as unpressurized Military Aircraft have service ceilings often up to 42,000 (P 51 & A4). In the similar designed ,Long EZ, pilot, Jim Price, in 1996 set an altitude record of 35,027 feet that still stands. (Biggest problem was COLD! He had ice on the inside of the canopy.) So unless you equip it with a Jet Engine (There is at least one so far!) pressurization is not a concern in this type. If you wanted to redesign it for pressurization purely for comfort reasons, the weight penalty would be considerable.
Contact Terry Schubert (firstname.lastname@example.org) Editor of the CSA, Central States Canard Association, newsletter for member/owners in your area.