It doesn't sound like a lot that way but it's around a 20% difference, that's quite a bit. The reason that I'll be getting a .45 is because after owning a .40 for a while it just doesn't seem worth it. It's more expensive, it has a lot more recoil, and 9mm ammo is more popular and easier to come by in SHTF situations. If I make more money in the future I'll probably get another .40, but for now I want a .45.
Also, the reason why I believe so strongly in weight being a big factor is because of a really long article I read a few years ago. It was a medical examiner talking about what he saw, and what worked good and what didn't. That article persuaded me to get a .40 and now that video I was talking about persuaded me to never use hollow points again. He talked about how they try to figure out what bullets were used by looking at the x-rays and usually when it was a huge amount of bullets("lead snowstorm") it was a 9mm or mouse guns. He also talked about how he wouldn't carry less than a .40 because of how many times he saw 9mm shots that should have stopped the BG but got deflected where as the .40 or .45 would just keep on trucking, plow through and stop the fight.