header & high flow cat
 

how hard are these two things to install if i where to buy & try to do the install myself?

In theory not hard at all, in practice, can be a bit hard. A lot of times with 11 year old exhaust systems you will find most of the bolts are rusted and hard to get off. You will also find the oxygen sensor is hard to get out. Some PB blaster, a torch, and a oxygen sensor socket will come in handy.

I would stay away from the no name brand headers, they tend to fit poorly, break easily, and rattle.

BTW there is no such thing as a high flow cat, unless you're talking about a straight pipe.. Catalytic converters don't have any moving parts, most OEM cats have 700 cells per square inch in the honeycomb, some aftermarket ones have as low as 200 cells, so in theory, that is higher flow I guess. In theory. But the universal ones can be a real pain sometimes, they may need cutting, welding etc..

I guess some cats have bigger inlets and outlets and lesser catalyst material like the universal ones but never actually heard of them making any power difference..