Exhaust Question?

Would there be a problem going with a 2.5 mid pipe into a 2.25 inch mufflers and tailpipe? The car is in my sig and is a street car with very few track trips. I already have aftermarket mufflers that are 2.25, so I was just thinking about replacing the mid-pipe. I plan on replacing the stock headers with aftermarket 1.5 units, since its an AOD vert, I understand that a little added back pressure will assist with the low end torque.

Future engine mods include a Tmoss ported lower, Thumper Heads, 1.7 rr and a 65mm TB. Havent decided on a cam change for sure but if I do, it will be the Crower 15511. Just providing this info incase it influences the outcome of the exhaust question.

I remember a few years ago in hot rod or carcraft mag. there was a guy with a BB Nova, that ran 3" mid pipe into a 2.5 cat back, his theroy was that the exhaust gas cooled as it traveled the mid pipe and that the smaller cat back helped with keeping the gas velocity high? Does that make any sense?

Thanks for the help.

Plan on running Dynomax Super Turbos. Getting old and need a more quite exhaust. Had them on my GT350 and liked them, I know there are probably others that make more power but as you can see by my future parts list, Im not trying to build a track terror or a street terror for that matter, just a nice ride with some more umphh.