The exhausts are the same except that 3.0 has twin tail pipes on the back box and 2.5 has just the one. GM factory originals with the nice pipe are no longer available. And all of the after market ones have a plain pipe. You can get after-market tail pipe embellishments if you feel the need.
The seller linked to earlier that had the 3.0 version doesn't seem to have a 2.5 single pipe kit for a 2.5 saloon, they do for the estate. However they do sell all the parts separately including the 2.5 back box.
I got a
one of these complete 2.5 V6 exhaust from a German seller a couple of years ago. It was fine. Thicker metal than I expected and it fitted perfectly. Made an offer and got it for £80 delivered. Took about a week to get here. This current seller seems to be Polish so not the seller I used, but the exhaust seems to be the same.
Of slight concern is that since then there is a lot less choice on ebay. And the price has gone up.