I had some 'temporary' aluminium hangers on the end section of my mk1's Janspeed exhaust for a good year or so.
I think the only reason they held up were because they were not directly subjected to an awful lot of heat.
(When I say hangers, I mean a selection of random aluminium sheeting and bolts that were the closest thing to hand when the exhaust started to fall off!)

If you want lightweight, Titanium is the only way to go, though with Titanium thickness is often a factor, as is cost.

Inconel provides the ultimate in durability and corrosion resistance, but it's pricey, and heavy. Typically around 8g/cm^3 (on a par with cast Iron).
Fantastic stuff for turbo manifolds and hangers which support weight whilst subjected to extreme heat (e.g. Turbo hanger to take lweight off manifold) but as Titanium is cheaper and lighter than Inconel-type alloys, I'd still go with a Titanium exhaust to go with the Inconel manifold.

Titanium is often obscenely priced when you consider the actual cost of raw titanium though.

In the coming months I may start investigating Nimonic and/or Inconel parts, as I may be able to purchase some tubing at near enough intrinsic cost (anywhere between £10 and £25 per kilo depending on exact alloy).