Bolt on's, when does it get counter productive?

tommyguns

I was wondering when bolt on's start to be counter productive. I'm getting ready to pull the trigger on a set of ART's, but I'm wondering if I've already taken the bolt on route to the max. I've just installed the M370, so now it's CAI intake, exhaust, manifold, flywheel and a tune. I'm just looking at my dyno chart before the manifold and it's 320/243 on a Mustang. Now I will say that I can definitely feel the M370 even without it being retuned so I know the mid torque is up. What if anything will I gain by adding the ART's and a retune. So I guess what I'm asking is, is it worth getting the ART's or at this point should I just retune and be done with it.
Thanks for the advice,
Tom

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09 Sport / MB / 6sd / Nismo"R" Intake / Eibach Pro Kit / Z1 25 row cooler / JWT LW FW / New Short Block 3/11/11 /H&R 15fr 20rr/DBA 4000/FI CB with 12"res./Morel/JL/"Division"mod/SPC/EcuTek/M370/ZEX C SHOT/ART's/NRG