Okay, I've got results. I'm on the April's 18th nightly build, everything's clean n' wiped and as stock as it comes.
With sim card in, I got an average of around 70 percent good 911 calls.
Without sim card, I got an average of around 20 percent good 911 calls.
I've done around 12 and 12 calls on each case.
I've never had to shutdown the phone, or no signal after 911 call, or magic reboots just because the 911 call. Nothing of strange things, just the call didn't connect and I'd to call again normally with no waitings of any kind or another troubles.