How are the MAC copper header gaskets?

I've used them without any issues, if you want something different look into the Fel-Pro 1415.

Never tried the copper ones, but I'll definitely second the Fel-Pro 1415's if you decide not to use them. They seal great and have a steel mesh inside them for strength. Plus, I've been able to reuse the same set of gaskets lots of times when I had to pull my headers off.

On the copper subject, I've been advised by people more knowelegable than myself that they aren't a good idea on fuel injected applications because there is a greater chance of small exhaust leaks which can throw off 02 sensor readings.