carbide or HSS?

[iowaboy.17]

I want to turn down some BIG drill bits; they must have 3/4" shank at least. I want to get them down to 5/8" but I only have HSS 1/4"x1/4" tools for my 12" swing Atlas lathe. Before I ruin the HSS bits I have, should I run out and spend some $$$$ for carbide? 99% of my work is on mild steel or brass, so HSS works just fine. I know nothing about carbide; are there good/better/best grades? Any comments gratefully received. tom