I'm sure it really doesn't matter either way whether they're alloy or steel, I doubt the weight saving would make a jot of difference to the people on here, It's not like you're F1 drivers looking for a 10th here and there is it ?, If I were to go down the front mount rout again I'd make sure I ceramic coated the manifold/turbo and down pipe and also fitted a turbo blanket before I ever thought about the boost pipes, With those I'd probably wrap them in some of that fancy silver tap to reflect as much radiant heat as possible.
I'd also wrap all the wiring in protective heat sleeves.
Rob