All depends on the heads and flow....The trend in cup motors has been get the intake Valve as big as you can get it and hang the exhaust open longer to compensate for the lack of size.

2/3rds (at least, some say) of the POWER a motor makes is on the INTAKE side.

What Andy says in terms of Bracket motors and single patterns is essentially true

Generally with a Bracket Wedge motor if you want a 260 degree exhaust lobe and take a 254/260 against a 260/260 and the bigger intake will almost always make a bit more power but it may be softer on torque somewhere in the band. It's always harder to Fill the hole than it is to empty it, air has to Fall in but it is essentially pushed out....i.e. it's basically already trying (gases flow from higher pressures to lower) to get out.