The average data rate will significantly go up. The Gigabit LTE solution around 7m Snapdragon X24 modem can offer speeds of up to 2Gbps. In reality you will get less than this peak maximum but it will still mean that 90 percent of operators will be able to get to a few hundred megabits per second on average.
The 5G based phones will be coupled with the Snapdragon X50. This is a 855 meets 5G X50 modem with super low latency at close to 1ms and speeds in multiple Gigabit per second. All of s sudden the peak speed with mmWaves gets to Multi Gbps with 5gbps mentioned several times during the Snapdragon Tech summit as one of the peak speeds. Bear in mind that 4G started at 100 mbps peak speed and achieved now a 2Gbps peak speed with the latest solution. 5G will get faster too.
Another part of the Snapdragon 855 wireless story is the new WiFi 6 ready that will improve for many verticals.
Another pinnacle is that the Snapdragon 855 supports WiFi 60 GHz that can take you all the way to 10 Gbps. This is a shorter distance, millimeter Wave solution that will enable some cool technologies such as immersive mobile eXtended Reality.
This is a significant improvement compared to the wireless capabilities of the 845, and you can expect to see this in OEM phones in the first half of 2019.