You WILL have overheating issues with any computer with a 675M or above, about - that's just a fact of laptops.
SLI compatibility should be a fair bit better now that drivers have had time to mature, but it may still cause issues in some cases.
As for 3d support, do you mean running it on a 3d monitor, or running in 3d itself? I'm not sure I've ever seen a 120Hz laptop panel, so I'd be very surprised if it could do it on its lonesome. You could probably get it running with a 3d monitor, but it's going to struggle with medium high settings at 1080p, so there's no hope for 3d with good settings and a smooth framerate.
Why does it have to be a laptop? If it's an issue of portability, I suggest going with a small form factor desktop. If it's an issue of needing something for school, get a cheap netbook, put an SSD in it, and build a computer.
What I'm trying to get at is that you can spend half the price and get double the performance or better, if you build a desktop as opposed to going with a laptop.