You could be there in just over 18 hours John.
No speed limits in Montana.
Alas, an oft-repeated fallacy...
On a couple of small portions of I-90 and I-94 this was/is true, but for the rest of the state there are, indeed, speed limits. Last summer I got clocked doing 87 in a 65 zone just North of Great Falls by an oncoming trooper. I paid the
$20 fine on the spot. If I had been written up for going 3 miles an hour faster (which, in fact, I was well in excess of), it would have been a 'point' and been reported to my insurance company. I did manage to make it from Minot ND to Missoula MT (750 miles or so) in about 10-1/2 hours, which is a pretty good indication of how fast a fella can successfully go in that state.
I listened to Overnight Sensation a couple of times on that trip...