Actually, the SAAMI spec'ed pressure is the same for both: 35,000 psi. 9mm +P and +P+ actually exceed .40 S&W pressures by a fair margin. .40 S&W also generates about the same, or slightly higher, muzzle energy than 9mm +P+ (400-500 ft-lbs). Recoil energy is higher for the .40 S&W, but not by a huge amount. Some ROUGH numbers from playing with a recoil calculator, assuming:
2.5lb gun for all,
Factory published velocities,
Powder charge based on Accurate Arms load data
9x19, 124gr @1,100 ft/sec, 2.63 ft.lbs and the recoil velocity is 8.23 fps.
9x19 +P, 124gr @1,200 ft/sec, 3.34 ft.lbs and the recoil velocity is 9.27 fps.
9x19 +P+, 127gr @1,250 ft/sec, 4.04 ft.lbs and the recoil velocity is 10.2 fps.
.40 S&W, 180gr @ 950 ft/sec, 4.31 ft.lbs and the recoil velocity is 10.53 fps.
.40 S&W, 165gr @ 1,150 ft/sec, 5.58 ft.lbs and the recoil velocity is 11.99 fps.
.45 ACP, 230gr @ 850 ft/sec, 5.3 ft.lbs and the recoil velocity is 11.68 fps.
.45 ACP +P, 230gr @ 950 ft/sec, 7.16 ft.lbs and the recoil velocity is 13.58 fps.
10mm Auto, 155gr @ 1,350 ft/sec, 7.26 ft.lbs and the recoil velocity is 13.67 fps.
10mm Auto, 200gr @ 1,250 ft/sec, 9.98 ft.lbs and the recoil velocity is 16.04 fps.
And for the curious...
.44 Magnum, 300gr @ 1,270 ft/sec, 22.47 ft.lbs and the recoil velocity is 24.06 fps.
Excess data aside, going from 9mm to .40 S&W isn't that big of a deal generally, unless the gun's design was of marginal strength for 9mm to begin with.