Wegen Gypsy Jazz picks! Made of frictionless material and last forever. I never would have believed it but I swear by them now. Definitely worth a try even though they are a little costly http://www.wegenpicks.com/#gypsy
you should definetly go with dunlop 0.60 mm, ther the orange ones, since your playing death metal you need stiff ones, and these are perect not too stiff not too soft, and they have great grip and normal size, they do m great. hope this helps
I've used metal picks (they spell death to your strings faster!) And for about 5 years I played with a pick made from marble. It was thicker and heavier. But it really improved my speed. Downfall to the marble pick is the noise it makes as it's striking the string. I quit playing with them once I started recording stuff. The other downside, $2.50 per pick.