The CPUs AMD just announced at Computex will be officially released on July 7th. Also, you have to consider the prices quoted are, most likely, MSRP, so expect a higher street price on day 1 (usually ranging from 0% to 30% depending on location and store).
As for performance, you only have AMD slides that say or mention a slight increase over Intel parts and a 15% IPC increase + ~7% increase in clocks over Ry2K. I do not believe there will be a 15% IPC increase across all workloads, so I'm willing to say there's bound to be an increase in performance of "up to" 30% on the very best case scenarios.
All in all, if you can wait then wait; benchmarks are the "do or die" for everyone looking to buy a new PC. On the other hand, even if you buy either a 2700X, 2600X, 9800K, 9900K or a 9700K you won't be unhappy with the purchase. You just need to make sure you get the most bang for your buck. Within certain price ranges and your base performance level (minimum requirement), you shouldn't worry about the next releases for gaming specifically. Personally, if you can buy a 9900K, then do it. If you can find a cheap 8700K, do it. If you can find anything Intel with >6 cores then you won't be disappointed at all (at the right price). AMD can be more of a hit or miss, depending on the offers, but they're generally cheap enough to free cash you can spend on a better GPU, SSD or more RAM.
EDIT: Somehow I lost half a paragraph, lol.
Cheers!