I'm just playing through this with my girlfriend right now, both of us are running Win7, though I've got an AMD processor on my end. We were having pretty serious crash issues for a bit as well, until we used BCDEdit to enable the UsePlatformClock option. To do that, you run a command prompt as Administrator and enter the following command: "bcdedit /set useplatformclock true". Then you reboot. Once we both did that the crashing became a lot less frequent, as did the weird sync issues we'd been having when driving.
One important note: we both are NOT using Powertools, since the BCDEdit setting fixed our speed problems. I suspect you shouldn't run the two at the same time, so try that first.
Another important note: the game WILL still crash eventually, period. We've yet to have a single session longer than a few hours where it didn't crash. Generally you can expect one every two hours on average, but that's ON AVERAGE. Could be three hours between, could be half an hour. SAVE AFTER EVERY MISSION AND EVERY STAGE OF ANY ACTIVITY.
One final thing that may or may not help: we've both used Nvidia Inspector to enable the hidden Framerate Limit option for the game's Nvidia driver profile, setting it to 30fps. We did it to fix some animation issues we were having with cutscenes (attachments detaching and floating weirdly), but afterward my girlfriend seemed to crash a bit less. You can do the same thing with Radeon drivers using a different tool (the name escapes me), but whatever the case adding a 30fps frame limit may help.