I understand that completely, which is why I stand by my point. Bore difference has a negligible effect on power. If however the stroke was greater on the 318, it would be a slam dunk, but it's not. Dress the 273 out with the same heads and induction and exhaust as the 318 and it will perform almost identically.
Same argument can be made with 318 and 340. Except, there is less of a difference in bore between a 318 and 340. 23 cubes difference between 318 and 340 (all bore), and 45 cubes difference between 273 and 318 (all bore).
