the old adage from the Motorola repeater sales literature was 100ft/100W/100miles... so if you have a 100ft tower with 100W transmitter you should be able to reach 100miles... however, that might be bit optimistic in real conditions, with mountains and such. ultimately you are limited by line of sight and the horizon, but with VHF you can go slightly over the horizon when conditions are right. also, this applies to analog voice (i.e. like we use on VHF business band now), with digital you can do get line of sight ranges with much less power, i.e. most satellite comms and cellphone is digital nowadays. e.g. the transmit power is much lower than 100W on satellite devices which is like in the 100s of mile range when overhead. i think many race orgs have rules that say the power is limited to 25W on VHF radios, I believe, but I bet many teams ignore that, but unless you have lines of sight having more power doesn't really help.
As mentioned Call PCI talk to them or visit their trailer at the races. They have the most knowledge and the great team there will guide you in the right direction for your application and budget. Also they have the best service of anyone in the industry. And might I mention The Weatherman the support PCI gives to our sport is top notch. WeatherBoy and WeatherMex are on top of a mountain right now getting ready to support many teams today that have no idea how much they will rely on the Weatherman team AKA PCI Race Radios today. PCI gets all of my race comm money.
There is no "best" - it's not the radio itself that makes a communications system good, it'sa combination of how the whole package is set up (radio unit/antenna setup/mounting/terrain/etc). You could have the most powerful unit available and still transmit less distance than a unit of half the power, simply due to setup.
As recommended, talk to PCI and see what package they believe works best. They are very experienced in the desert racing scene (some would say the Subject Matter Experts), and will be able to give you the information you're looking for.
the antenna is just as important or more than the radio. You can get the best stuff from PCI and still have crap signal.
Make sure the antenna has a good ground plane. make sure all the wires are away from interference, good connections, and as short as possible.
Also make sure your radio has good enough power source and gauge of wire. I see lots of 50watt radios wired with little 16guage wire and thru a cig lighter. You won't get the current you need that way. You need at good source and large wire. We upgraded our race truck radio power system and get way better range. Its amplifier and should be wired as such. You would not put in some big audio amp with tiny wires.
Its not just what gear you have but how you use it