Full exhausts to open headers gain

We have a 3800lb car that currently runs a mild street/strip BIG wedge motor, best this year so far were 10.3's@129-ish, has gone best of 130 with full exhausts. It has 2.18>2.14" TTI step hdrs 4" collector with 2.5" pipes to the rear, not sure on the muffler make. The heads are -13's 365CNC, cam is small s/roller with 260/[email protected] and runs a good working but small 950HP carb. Stall is 4200-ish with 4400 being max torque on motor, car hooks and goes 1.43 60's best to date with caltracs/mono's.
Apart from the weight (50lbs?) loss have any of you run with exhausts and gone open, if so what was your gain and what can be expected on our set up with info given, whats your estimates guys, up jetting of course will prob be needed....bit of a how long is a piece of string question but lets see what you say.