Are there any differences between the various downpipes. Is there any reason to spend the extra money for a Corsa downpipe?

I think you are talking about front pipe's (or cat delete pipes). If that is what you are talking about, any aftermarket front pipe will work. All cat back systems have to bolt up to the 4 bolt flange, so any MBRP, Diamond Eye etc..front pipe will work. No use to pay the added $$$ just for the Corsa name

for the 05 LLY- If you get Silverline full system the front pipe slips into rest of pipe(no 4 bolt collar)like MBRP etc.

for the 05 LLY- If you get Silverline full system the front pipe slips into rest of pipe(no 4 bolt collar)like MBRP etc.

He has a Corsa Cat Back, so in his case he would have the 4 bolt flange.