well I figure the stock catback off the SRT8 would be probably larger diameter with a more straight through design while still maintaining great sound levels.. while most or all aftermarket or custom exhaust while sounds GREAT while putting your foot into it.. sound terrible when MDS kicks on, and that's where the drone is... as for power, there might be some gains but no more then 15-MAX - same with the intake 15-MAX ... also make sure you keep an xpipe in the mid.. if you don't, you will lose power.
as for intakes your choices are Volant, AFE, mopar and K&N ....
Volant - sometimes has fitment issues and they are quieter.
Mopar - is solid but there's gaps around the intake tube and the heat shield which I feel makes the heat shield pointless. It also mounts to the power steering reservoir which I think is a terrible idea.
K&N - while they make great products and I use their oil filters, I feel slacked on making this intake, they just make it functional, nothing more, nothing less to really make it stand out.
except for their oiled filter. which to some is a drawback.
All these reasons led me to the final one,
AFE- the tube has the largest diameter out of all of them, the tube is also metal coated in a rhino lining like material, which I feel makes it look fantastic. The heat shield is constructed well and functional and mounts to existing intake mounting points. it also has a choice of oiled or dry filters... I chose the Dry filter
Side note- Put a larger throttle body on with w/e choice intake you go with.. they compliment each other greatly.