How the tiers are set
We place every graphics card in a tier by its performance index, where the RTX 4090 is 100. S is 70 and above, A is 50 to 69, B is 30 to 49, C is 18 to 29, D is 8 to 17, and E is below 8. The tiers are bands of real performance, not marketing names, so a previous-generation card can sit above a newer cheaper one.
The index is our own estimate of gaming performance at 1440p. It is built from specifications and public benchmark knowledge, and it is reviewed when new cards launch. Two cards in the same tier are close enough that price, memory and power should decide between them.