Standard exhaust power

I'm running an after market pre mapped ecu and 1 bar loop and was wondering what power I could expect if I fit a standard exhaust? Currently about 280-300 bhp. It's just I get sick of the drone from the aftermarket 2.5 inch exhaust. Also can you get these from anywhere nowadays ??

You will struggle to get one now I imagine,  especially the downpipe.

Have a cat back system made up the same shape as the standard system with the big back box and it will be quiet.

I have a 2.5" magnex like that and it's very quiet but also hard to get a hold of now I imagine.

People come up with stuff all on my to do list. I have a full standard good condition system and my exhaust builder is willing to copy it but i want to use a company up the road who are best availible but price will be trebbile

i've got a scorpion backbox and its very quiet compared to a mongoose

What have you got on there at the moment darren is it a goose ?

Not sure but it's something like that. As everything on my car is standard apart from blow off and ecu (will change blow off when I come across a standard one) then I think a standard exhaust would finish it off nicely