GPUs are much better at mining cryptocurrencies compared to CPUs, although not better than ASICs for this purpose. Well, there are many reasons you might want to mine cryptocurrencies with CPU instead of a GPU such as cost issues because a GPU costs more initially, and uses more power or has a higher power draw than CPU, but it will be much more efficient in the long run and will render more hash power than a CPU and therefore more profitable. On a normal setting, you would expect a mining rig that comprises of two to multiple CPU or GPU cards combine together to improve effectiveness and outputs. Some aren't profitable alone but will work better when combined but some are, alone.
Whether you use a GPU, CPU or ASIC may depend on the select coin you wanna mine, as much as it would depend on your profitability goals. Some coins do not allow GPU, some allow both GPU and CPU mining. But there is a wide variety in both cases. For instance, some of the coins you can still mine today with CPUs include: Monero, Bitcoin Cash, Dogecoin and ZCash among many others and with GPU, you might consider mining Bitcoin Gold, Aion, Energi, Zencash, Zclassic, ETH, Ethereum Classic, Bitcoin, Monero, Ubiq, Bitcoin Diamond, and many others as well.
With online mining profitability calculators, you can get a glimpse of the amount of profits you would expect when mining a certain crypto that employs a certain mining algo with a certain GPU/CPU/ASIC and hashing algorithm on the fly, although these calculators are far from perfect because profitability has to do with among other indeterminacies like future prices of coins.
And because the GPUs cards cost less and save more power compared to ASICs, GPUs are popular in the cryptocurrency mining arenas. Of course, an ASIC card will deliver a very high hash rate for specific coin due to the fact that it is much smaller and lighter for similar performance, and has a higher profit margin compared to GPUs. GPUs are, however, more flexible in their applications compared to ASICs, which are application specific for a given coin.
That said, there are GPU cards specifically made for mining cryptocurrencies and Nvidia and AMD are still the most popular manufacturers of GPUs used for cryptocurrency mining.
If you are assessing performance, the criteria are almost the same when accessing performance. You are going to look at power consumption, which will affect performance, noise output, and reliability; hash rates; memory, speed, etc. Remember to also consider the resale value: if the card can't play games good, then it may mean the resale value will drop significantly if you find it not worthwhile for mining crypto or want to dispose of it later.
A miner's hash rate performance will depend on the type and the version of the miner used as well as the type of VRAM used, and other factors. Therefore, even if values are quoted in this article, they are far from ideal for later versions of miners, software, and VRAMs. Miner versions and software versions keep coming up. These values are only meant as guidelines.
AMD Radeon VII
The AMD Radeon VII is AMD's high-end graphics card, which introduced a 7nm GPU architecture or process node into gaming and now, crypto mining. This architecture allows it to be faster than its earlier models. AMD said that the new 7nm allows the device to increase performance by 25% overall over last year's model without having to draw more power.
Launched in February this year and becoming available in retail centers last month April, Radeon VII renders a hash rate of 90 MH/s without any overclocking or with stock settings, which is 50% more power compared to Vega's 64 MH/s for crypto miners with stock settings. It is also around 30% faster than the Vega 64.
Radeon VII has 16GB of video memory (VRAM), memory bandwidth of 1TB/s, Base or Core Clock of 1,400 MHZ, and a boost clock of 1,800MHz. The GPU comprises of 3840 stream processors and it has a power rating of 300 watts. It delivers 10% more in peak engine clock compared to the RX Vega, and given its open air cooler and revised SMU, Radeon VII can boost to and sustain its higher clockspeeds often. It has 4 lesser CPUs compared to RX Vegas and same ROPs, but delivers more throughput across the board.
Radeon VII also doubles the memory size and more than doubles the memory bandwidth of the Vega.
According to recent tests done by VoskCoin with the Radeon VII for mining different cryptocurrencies, it could manage an average hash rate of 90 Mh/s at 319 Watts when mining Ethereum with the Ethash algorithm. Phoenix Miner 4.2c, which is the latest stable release version of the miner; manages a 2970 H/s @ 245 Watts when mining Monero on Cryptonight R. Other results were published on this medium link or as shown in the figure below.
In comparison, RX Vega 64 manages 32 mh/s with stock configurations when mining ETH on the same miner, according to a report by Wccftech, while Titan V manages only 69 MH/s and Radeon VII 100MH/s when mining ETH. That's even as Radeon VII is cheaper than Titan V (which is within $3000 range) while achieving a higher hash rate per watt.