Headers make a difference?, Headers? "High Flow" cats? some one help! 94 ST Options

[mgnt232]

I Have a 1994 Toyota Celica ST 1.8L 7A-FE
I recently had a Magnaflow "catback" installed.

I was looking into getting headers when i came across something interesting.
I saw that in order for the headers to give you car the extra power, you need to have a high flow catalytic converter. I am not sure if this is true, but i believe it is because the extra flow, from the headers would be slowed by the restrictive stock cat? am i correct? (the cat back is not restricted any more, with my new magnaflow exhaust system)
And if this is correct, would these two things match up?

The cat i am looking at ( http://www.planetmagnaflow.com/mfcatsearch...catmodel=CELICA ) !*The first direct fit one*!

The headers i am looking at ( http://cgi.ebay.com/ebaymotors/ws/eBayISAP...alenotsupported )

Are headers worth it? do i need the new cat? would it be better? with the new cat, is it worth it at all? ive never seen the difference, but im assuming alot of you have, so any one with any info, please give me some answers. thanks!-

[Random_Stranger]

Here's a stupid n00b question. I noticed when people get headers, they never have a cover on them, but either bare or they are wrapped. So my question is, can you still use the shield on them that comes on the car OEM? I noticed people use them on turbo application cars, so if your cat back system is 2.5", can you just bolt those on? Because now I am thinking about looking into this, or I might just wait until I actually become swapped.