If the weight and velocity of the shot of a high pressure load and a low pressure load are the same then the recoil is the same.
100% correct, pressure does not enter in the formula for calculating recoil. Max chamber pressure is but one component of the total barrel pressure. Pressure is applied from ignition, before the load starts to move, until the load exits the barrel. It is of course not a constant, but a curve. If you push the same load (include everything that goes out the barrel, shot wads & powder) to the same velocity then you have done the same amount of work. While the peak/max chamber pressure may vary widely depending upon the burning rate of the powder, the total pressure under the curve for the length of the barrel will for all practical purposes be the same. Thus recoil & the force against both the wood & the shooter will be equal.
A quick perusal of a loading manual shows I can easily find a 1oz load with 1200 FPS velocity @ a max pressure of 10,600 PSI. I can just as easily find a 1Ľoz load with 1275 FPS velocity @ max pressure of 8,200 PSI. Fire them both out of a 6-6˝ lb 12ga & then tell me which pounds both you & the wood the most.
