Why would you need chains and cassettes that cost in excess of 300 dollars?
You're a professionally sponsored racer, money is no object and you want to cut every gram of weight possible.
You have way too much money (generally, people who buy top end equipment fall into this group).
It looks cool among a certain crowd.
In picking your cassette, I'm assuming that (a) it is the right number of speeds for your shifter and (b) your derailleur has enough capacity to use lowest gear. If this is the same sized cassette as you had before, this should be satisfied.
The PG-1070 is a 10 speed cassette, so you just need a SRAM 10 speed chain (PC 1031, PC 1051, PC 1071, PC 1091, PC 1091R) [KMC also makes some SRAM compatible 10 speed chains if you choose to go that route, but the SRAM chains are reasonably priced and might work a bit more smoothly, so I don't see a point in going non-SRAM.]
The differences in chains are highlighted on their product pages, usually some of the metals used on some of the plates or a bit of weight. They may also shape the plates slightly differently to aide shifting performance. SRAM recommends the PC 1091 or PC 1091R for Red group use, but you can use the others as well.
Generally the differences are minor if existing other than a bit of weight in the cassettes and chains, but manufacturers suppose that people who buy expensive parts in the beginning will replace them with just as expensive parts further down the line (see the "looks cool" point above).