The 245 width is 20 millimeters wider than the standard 225 width. The extra width will be split evenly on the outer and inner wall of the tire, so you'll have an additional 10 mm of width inside the wheelwell. That's 1 cm or approximately .398" in extra inner wall width. I'd be shocked if they don't fit.
The standard setup has an overall tire height of 26.757". Your new setup would have an overall height of 25.761" . Overall, the new setup will have a slightly lower profile (about 1"), and will probably cause your speedometer to read slighty slow - should be negligable, maybe .5 mph or 1 mph at worst. Good luck.
I prefer that calculator since it's easier. It says indicated speed of 65 would be actual speed of 62.6, so yeah 62.58 is right. Not that much off, just a few more miles on your odometer. I'm actually running 205/40/17s right now, the ride is harsh as hell for a 3800# car but it's only until I feel like spending money on new tires.