Well, the technical and absolutely correct answer is that it depends on what bullet you're shooting (both weight and style). I suspect, at 3200fps, you're shooting 180gr bullets, as that's about what I'd expect from them. Using the 180gr Hornady Spitzer commonly available in factory ammo, you're probably getting about 3250fps of real muzzle velocity. If you're shooting something like a 180gr Remington Core-Lokt, you're about the same. If you've got some 180gr Nosler Accubonds, then you'd be looking at about 3240, which is, as you suggest, negligible in difference versus the others. It's also pretty moot considering the 3200fps you're getting at the chrony.
You can use any ballistic calculator to 'back-figure' the true muzzle velocity by measuring the velocity at 20 feet and setting it up to match that in the ballistic calculator.