exhaust question

I have just finished a set of 2" primary to 3.5" headers to go to a 3" short exhaust system. Now that I am building a 470 procharger motor I am thinking about sepping up to 2 1/4" to 4" headers while still using my 3" Borla xr mufflers. Can I step the exaust pipes down one inch over say a 5 foot run? Or should I go to a larger muffler and try and keep the pipe the same as the collector? This will be street strip so I dont want the loudest system.