i might be getting my car (mondeo zetec turbo) rolling roaded on friday

at present its got some very heavy 19" wheels on, should i swap the wheels over to my 18" lightweight dymags for the day or wont it make much difference?

i'm guessing the lighter smaller wheels will give less of a transmission loss and help the engine revs spin up quicker? or is the difference going to be neglible?

as long as the flywheel power isnt effected i'm not too bothered.