equal lenght will help in terms of spool etc as you have equal amount of exhaust gas pulses per cylinder thus a consistant speed in the turbo all the way through the rev range.
theres plenty of unequal lenght manifolds that work but they will be built on the cheap .
theres certainly nothing wrong with it but i bet you a £10 steve that if you built a proper equal lenght merge collector manifold you would have gains across all the engine.

cheers paul