Sadly a lot of guys fall for the glossy adds and fit the big exhausts with no gain and and a light wallet.
For it to work the hole system must be matched, intake, fuel, boost pressure and dump pipe all need to be evened out, not just 1 item, it can work against what is being achieved.
In your case drover the exhaust guys did a great thing for you. More $$ for trips away.
As for me, the tugs 3" exhaust is getting married to the new air intake, new intercooler and pipework with a slight increase in boost pressure.
That should be enough for me, I'll gain about 100nm of torque with just that, the tug dose have an old safari chip fitted, and the diesel guys think it will work well with the exhaust, intake and boost pressure. The last owner had it fitted on poor advise and had to de-tune it due to excess fuel consumption and no gain. It is a situation where it wasn't a matched system. When the injectors etc are finished, we'll look into re-tuning the chip. I want a "Towing Package" and am not interested in crank snapping power, those days finished in the 90's for me.