We have driven to the Grand Canyon from LV and it is 288 miles one way to the South Rim. Yes, the speed limits are high, but it is a very long day.
We have taken Gray Line Tours to Red Rock Canyon, Death Valley and othe places that I cannot recall at the moment. We've gone to Laughlin on Cactus Jack Tours because we had a free coupon with our airlines and that was okay. We took a lesser name tour(cheap one) to the Hoover Dam on our very first LV trip and the air conditioning did not work on the bus and we thought we would have to push the bus back to LV. After that, we started taking Gray Line Tours and discovered they were a class operation. Their drivers are very informative and some can be quite entertaining. We have always found them to be very pleasant.
Hope this helps.
Beth