One useful resource is www.carveryachts.com, and look up the model specification PDF files for the 1997 model year. I specify 1997 because it is the only year in that era that Carver published fuel burn specs.
For 1997, the Aft Cabins in your size range are 355 and 405. The Carver specs say:
355 - 19,300lbs, Crusader 454XL, 3,200RPM, cruise 21 MPH, 24 GPH (0.875 MPG).
405 - 27,108lbs, Crusader 454XL, 3,200RPM, cruise 22 MPH, 30 GPH. (0.73 MPG).
Santego 38 - 18,700lbs, Crusader 454XL, 3,200RPM, cruise 24 MPH, 26 GPH (0.92 MPG).
And just for fun, I looked at my boat for the '97 model year:
325 - 15,100lbs, Crusader 350XL, 3,200RPM, cruise 21 MPH, 22 GPH (0.92 MPG).
OF course, these figures are subject to a lot of factors, but one would think that the differences between the boats would be constant, regardless of what factors may influence the actual figures. So it looks like aft cabins have a slight lower fuel mileage, but again, they look to be a bit heavier.
My guess as to why the Santego 38ft (with a heavier boat and larger hull) matches my 32ft boat in fuel mileage is perhaps my 350CuIn engines are working a bit harder than the 454s.
Nevertheless, all of the mileage figures are pretty close together.
I have neither been aboard a 355 or Santego 38, but judging from photos, I'd dare say there may be a bit more room in the 355. Afterall, the "poop-deck" on the aft cabin offers two levels of occupancy.
Cynically speaking, maybe the best boat for fuel consumption is the one that has the largest holding tank - as if the boat is a gonna be a floating condo, that means fewer trips to the pump out. [8D]