+1 to Gold Dot being "thick plated" -
http://www.speer-ammo.com/products/gold_dot_const.aspx
As to variations in load data, you need to look at all the testing variables used to measure chamber pressures for the published load data. When I saw start/max charge discrepancies that were significant between powder manufacturer and Lyman #49 load data, I looked closer to the details.
Lyman #49 on page 362 lists the 4" Universal Receiver's groove diameter as .401" instead of the typical .400" for .400" diameter jacketed 40S&W bullets and the load data for W231 shows higher powder charges than Hodgdon load data (probably due to more high pressure gas leakage around the bullet). BTW, Speer TMJ bullet used is a plated bullet.
Lyman #49 load data - 4" barrel, 1:16 twist, Winchester SP primer:
165 gr Speer TMJ W231 OAL 1.120"
Start 5.2 gr (937 fps) -
Max 5.8 gr (1050 fps )
Hodgdon load data - 4" barrel, 1:16 twist, Winchester SP primer:
165 gr Sierra JHP W231 OAL 1.125"
Start 4.8 gr (946 fps ) -
Max 5.3 gr (1001 fps)
Add to this different bullet type, pistol barrel lengths, groove diamter, leade length, rifling type, recoil spring rate, primer and OAL used ... you may deviate from published velocities/pressures quite a bit. Hence, I tend to lean to the side of safety and not try to push my luck too much.
YMMV