Exhaust help! 5.7 vortec plugged cats..worth paying for larger diameter replacement??

[HeavyD]

So I bought a pretty clean (for here anyway, no rust etc) 98 z71 with the 5.7. Got a PO430 code and after replacing the O2 sensors friend suggested it is time to replace the cats which have lived for 277000km.

I know the factory piping is pretty tiny, but is it worth it to have a slightly larger set fabbed up? Can find stock replacement easy enough, but nothing larger, say like a 2-1/4. Would there be any real gains?

Headers worth it? It is a winter daily driver so I am not sure how much I want to spend on this thing yet. Other than changing out the poppet injector arrangement it won't see any engine mods.

Looked into a 3/4 ton setup which is larger, but shops here say it can't be used as it is different, even though the truck body and engine is the same? confused..

So is it worth it to spend some coin in this area? Having a shop fab a complete system up will prob be over $1000. Stock replacement of bad area about $500.

Anyone?