I saw your update and that you were going with the 12x42's and I trust that you've made the best decision.
The difference in magnification is so subjectively perceived and it really depends on what you're viewing and what level of detail your trying to achieve.
Switching back and forth between a 10x42 and a 12x32 is quite noticeable while siting up on a mountain and doing comparison views of the same objects. There's no question that the 12x have an edge and this is apparent even to my less experienced binocular users. While I use the word "noticeable" the difference isn't always "helpful" and the same can be said when switching from a 8x32 to a 12x32. While there's a definite improvement in the amount of detail that can be seen on a distance structure for example, if you're trying to resolve smaller details, like a distant sign, or trying to count the points on an elk at 1000 yards, or seeing bullet holes at a distance, the additional 4x still might not be able to do that. My common, two binocular option is usually the 8x32SV and the 15x56SLC HD used on the ultralight Vanguard VEO 204CB, while seated. My outdooring buddy kind of came to the same conclusion I did after having tried a 8xEL and a 12xSV for a season. He agreed that if he was going to carry 2 binoculars, they should have as much separation as possible in order to avoid too much capability overlap. Sometimes even the 15x's are quite enough if you're trying to judge details on animals at distance, but it's significantly better than the 12x. In typical lighting, I have a lot of difficulty seeing .22 cal holes on black paper at 150-200 yards but they can be viewed without too much trouble using the 15x. So again, it just depends on what level of detail you want/need to see and if the idea is to just get the most beautiful and pleasing, overall image that you possibly can, while enjoying just a little bit more magnification, you might have made the perfect pick.
With all of that stated, the Canon IS and particularly the 10x42 version, will provide significantly more detail while viewing handheld, than either of the Swarovski's. It's just physics. While you can certainly enjoy a huge, perfect overall image while using the non-IS bins handheld, they just can't compare to the IS Canon's when it comes to seeing fine detail in the eye's, feather's, whiskers or individual hairs on an animal. The same goes for reading distant signs, license plates, aircraft N numbers, or when trying to count tightly bunched numbers of objects.
I have a little backyard demonstration that I share with binocular users, where I have them them look at a powerline tower that's about 275 yards away. I tell them to look a the top of the tower where the angles converge and are bolted together with relatively stout 32mm range hardware... and all spaced relatively close together. I ask them to tell me how many bolts are on the main tie, while hand holding any non-IS binocular that I own or they have brought with them. Despite some people being more naturally steady than others, out of about 25-30 people, only one was able to tell me the right answer, which is 12. This happened to be a person with a 12x Ultravid but that's not the point. Then end of the demo has me handing them the "lowly" 10x30IS II $399 (when I purchased mine) and I tell them, "try again with these." Usually it's only a matter of seconds before they say, "there's 12!" .... That's amazing! ... "I see what you're saying" ..."Wow!" and other similar exclamatory language. Obviously, detail is only one aspect of the view but the Canon IS are the kings of seeing detail, while hand holding. For reference, I've owned 6 different Canon IS bins and currently own the 8x20, 10x30II, 10x42 and 12x32.
The great thing is that you always have the option to use a tripod if you need to see the same or even better detail, through the Swarovski.
