Total induction length dictates the power curve on an engine. If you stick long ones on it should produce more torque, shorter and it will produce more bhp. Forumlar one cars can extend theirs comming out of corners for more low down power. The Omega V6 lump is built to produce lots of low down torque so naturaly would benifit a lot more from a long induction length than a revvy four-pot would. However if the plan is to start camming the V6 to rev a lot then you can bring the induction length down.Ya know that Astra with the V6 and TB's.... if (ignoring the physical limitations) it had much longer trumpets.... would it perform much better????
It really comes down to how you wish to drive the car, TB's such as the SBD ones are tailored to the kit car racing scene therefore are designed to produce lots of bhp and the power band is all at the top end as when racing on a track you spend most of your time at high revs.
For a 'streetable' engine you would get more 'performance' from longer trumpets, especialy on a V6.