[lunarhighway]

i think the main reason for the bifferent bumper is that the golf was a long running model that needed a new face... aerodinamically it might incorporate more of an airdam than the original "clasic" configuration, but with the adition of an airdam i think both setups will likely be comparable. the main thing indeed would be a front undertray.

also with a front undertray a very low airdam might not be needed. aerodynamic modern cars often have a raised airdam in the center, alowing a more smooth transition to the undertray, rather than be harch to the air. so if you go for modern aero, the old bumper might give you more freedom, while the "modern" bumper has the 'low tech' airdam function build in (vs more advanced undertray)... on the other hand, you can't be sure untill you test it that with a relative rough underside, a classic airdam isn't better than a partial undertray... or that perhaps the plastic airdam provides easier undertray attachment...

the advantages of the newer bumper might be better crash protection, to a small degree... and also cosmetic protection (the lower metal work might dent but the plastic might not on a minor impact, and if it's destroyed it can be replaced)... not fe related, but something to take into account perhaps.