At just $398, about the same price as the cheapest GeForce GTX 1070 you can find, or $478 for a pair of 8 GB cards like those we have, Radeon RX 480 CrossFire is not a viable solution if you plan to buy two cards upfront. When averaged over all our games, it is consistently slower than a single GeForce GTX 1070 at all the resolutions that matter - 1080p, 1440p, and 4K. Instead of buying two cards upfront, you're much better off putting your monies into a single GTX 1070, not just for better performance but to dodge the spectre of application multi-GPU support, which continues to haunt both SLI and CrossFire.
We averaged games that do take advantage of CrossFire in a separate relative performance data-point than the overall relative-performance. The findings are interesting; when averaged among games that do scale, the RX 480 CrossFire is about 5-10% faster than a GTX 1070. However, only 6 out of 16 tests are taking advantage of the second card.
If you only have money for a single card now, and you want to buy a second card later, you're in for more than playable frame-rates at 2560x1440 resolution in games that do scale, and even 4K performance with eye-candy watered down a little. RX 480 CrossFire loses out on its overall relative performance big time due to the number of games that don't scale well (6 out of 16).
In games that do scale, you're treated with upwards of a 85% performance uplift. From our Radeon R9 Nano CrossFire review till now, we see that AMD hasn't really spent a lot of time optimizing CrossFire for more games. We can't fault AMD too much, though, because since then, a lot of games that came out don't support multi-GPU at all due to engine limitations. There's not much AMD or NVIDIA can do about such games, and this is what scares us about multi-GPU solutions going forward.
We have to give AMD credit where due for including support for 3-way or 4-way CrossFire, unlike NVIDIA which has dropped support for 3-way and 4-way SLI. The RX 480 supports both 3-way and 4-way configurations, and in any application that can take advantage of CrossFire, not just synthetic benchmarks.
With the advent of DirectX 12, we are promised new multi-GPU rendering modes thanks to Microsoft giving developers more control over per-GPU resource allocation, but we doubt that we'll see widespread use of those techniques. Nowadays, games are developed for consoles first (which are single-GPU), and publishers have little interest in spending a lot of developer time (= money) on adding support for exotic multi-GPU configurations that are used by only a small percentage of their customers.
Some of the latest DirectX 11 games (eg: Just Case 3) and the early DirectX 12 ones are struggling with multi-GPU support. NVIDIA too, has cut out 3-way and 4-way SLI support (but for slightly different reasons), making us wonder if it's worth the trouble to follow a multi-GPU upgrade path with mid-thru-performance segment cards such as the RX 480. We rather recommend you spend $398-458 on a single GPU solution.