The drive to Las Vegas from LA is 90% in California. In California the limit is 70 from Vitctorville on. Driving 75 you won't get a ticket. Driving 80 you PROBABLY won't get a ticket. Anything over 80....depends how lucky you are and how good your radar detector is.

Inside Nevada, from the state line to the southern outer limits of Las Vegas, speed limit is 70, not 75. It's only 75 on I-15 north of the city. Once you hit the southern suburbs it's 65.

FYI...there is a new highway in Texas, outside Austin where the speed limit is 85. And on some section of I-10 and I-20 in TX the limit is also 80. That's the highest speed limit in the country right now. Utah experimented with an 85 speed limit on some portions of I-15 but it was lowered to 80.