I believe the SAAMI specs for the max operating pressure of the two is 35,000 for the .40 and 37,500 PSI for the 10mm Auto.
I run a 20 pound spring in my G20 with a KKM barrel. Never saw a use for a .40--that cartridge is a solution is search of a problem in my opinion and if I had my way it would fade away into obscurity. The more useful cartridge of the two, the 10mm Auto, got screwed in the popularity contest. But I think that considering it lacks the military history and nostalgia of the 9mm and .45, and the brand name and commercial support of the .40, it has done alright for itself based purely on it performance. People said the 10mm was dead two decades ago at least, but it continues to have a devote fan base, myself included. I don't think it will ever be mainstream, but as a Metalhead, I am okay with that. Pretty much everything mainstream sucks, including the .40 S&W.
I like the Doubletap stuff. Mike does it right. The 180 gr Gold Dot load is awesome. I also like the 175 gr Silvertips as a good moderate standby load. I know either of these loads will let you know you touched something off. They can be a little snappy. But they aren't abusive and the thing that always strikes me about my G20 when I am shooting it is how much I feel like I am getting something for nothing--more performance, more blast, more fun, and more utility--with very little in the way of added recoil or expense. I have seen a 16 year old girl run my G20 with full power 10mm and her smile when the slide locked back was almost as big as my own smile when the slide locked back after my first mag through the thing. I just try to remember it is an autoloading .357 Magnum, and I treat it as such, so I don't expect .1 sec split times.
The only .40 I've ever shot was a friends SIG Pro. Maybe it was the change in the grip angle and the higher bore axis, but it definitely seemed snappier to me. In fact I dumped a mag through it then handed it back to him and told him to keep it, then went back to shooting my 10mm.