[Neutrino]

curtis is right on the money, this is why modern high tech engines use variable length manifolds (Ferrari seems quite fond of them) and variable timing and lift valves (as the ubiquitous vtec) you get the best of both world.

Same reason I'm a fan of variable geometry planes.

If i may add something on turbos however: the larger the pressure diff between the turbo manifold and exhaust the better. Faster moving gases in the exhaust should (in theory) create the same low pressure area behind the turbine which will increase the pressure differential benefiting turbo spool.