This is something that I do on my GF car and here is some short review.
Do to her automatic transmission several changes have not being done, so the car will have more power.
Header == SPOON
By far its the best header ever. The one in the picture above doesnt even look like SPOON (more like GD1) Spoon version are very smooth and nicely build. Off course there are others such as Xforce, Mugen, J' Racing, Malaysian (HotBits) and several local brand. Which uncomparable. I say go with SPOON!
Downpipe == Custom
Well the arent too much alternative and in my case I got a very good quality version made in thailand. Compare to Xforce, Mugen, J's Racing, and Hotbits etc. Changing your downpipe doesn't really make a different because u basically try to remove the Catalic Converter to boost the power
At first I didnt change the downpipe and to be honest it really make a different in performance. However it really boost the DB level of the sound inside your car.
B Pipe == Standard
Again since I'm running on auto this is the less thing you want to change. Since removing the Catalic Converter will surely make the car loose its power and further increase the DB level. However if you want to make it look nice then surely change this will make the cosmetics looks good.
Exhaust == HKS Pro
Well, the best bang for buck. However several brand do make a better product. However most of them just look better and did not adjust the performance. However there are one brand, which I believe do make the best Exhaust (J's Racing) which made by Titanium in this case very light .5 KG compare to mine 5KG. hehehehe...
Overal changing your exhaust system will not be maximum if you didnt change your CAI too. So, please do change it. Maybe I'll make some review later on about the best CAI for our hamster.
Hope this help.