one thing about the tune that might make sense to tweak after long tubes is a table called hego delay. it essentially helps the computer determine when to check the voltage at the hegos when it is in closed loop. this is how it checks to see if the amount of fuel it commanded was correct or not. with long tubes, the O2 sensors are usually moved farther away from the exhaust ports than stock, so a good tuner will adjust that table as necessary for long tubes.
without that change, the computer will have a hard time dialing in the injector pulses to get the air/fuel ratio correct. will it be noticeable? maybe, maybe not ... depends on how far they were moved and probably other stuff like spark timing ... there are too many variables to be able to say with any certainty
I would ask a tuner what they would charge to only adjust the HEGO delay as Chris mentioned. That could be done in 15 minutes or less with no dyno time needed. But that would require a tuning chip or device which I'm sure you already have.
Assuming you have a chip, you will need a re tune. Your current exhaust is way too small and the new one is a lot bigger/better and your a/f will definatly be out of wack. This is another reason I prefer self tuning.