What is Copper's integrity after high heat?

When I fire copper, brass or stainless steel with metal clay what
effect will it have on the copper/brass/stainless pieces (besides
oxidation)? Will they maintain their strength? Or will they become
weaker/brittle like I’ve read about sterling that is fired at the
high end of the firing temperatures? I am using pmc3, heavy gauge
(3awg) pure copper, regular red brass (tubing) and "un-pedigree’d"
stainless- I would like to fire these things at the highest
temperature for the longest time for maximum strength-1650 F for 2
hours. The minimum firing temperature and time are 1110 F for 30
minutes would this cause a problem with the included metals?

Thanks for any and all help.