HP gains and header question

[speedsters9]

I recently upgraded my stock intake to an AEM CAI (highly recommended upgrade)... my ignition system is brand new OEM, with performance wires and NGK copper core plugs. I found the copper core better than the iridium ones...Last year I replaced my thunderpipe with about a 1/4" larger diameter pipe and am looking at adding a performance header when I replace my oil pan gasket, and change my timing belt. What diameter and type (ceramic) of header do you recommend and what would I get as far as hp increase... ie 4 - 6 hp or so?

I will replace my stock muffler with a stainless one that hooks up to the thunderpipe just anterior of the right rear wheel... this kind of a muffler should give another around 2 - 4 hp. So am I right in figuring a total hp gain of something like 16 hp with the CAI, header and muffler.

and once the muffler is added if I bore the throttle body would that add another 2 or 3 hp?

thanks