Wait for Better Performance (& Android 10)
The OnePlus 7 Pro comes with tons of RAM, and a new internal storage type (for the 64, 128 or 256GB of space) that's faster than most phones already on the market. That's what makes it feel and run so quick compared to other devices, the UFS3.0 storage.
However, it can and will get even better when the OnePlus 7T comes out. That's because it'll potentially have even more RAM, the latest Snapdragon 855+ processor (not the regular 855) and be running on Android 1o. Furthermore, it'll be the first phone to run Android 10 out of the box, which is awesome for buyers.
Obviously, older devices like the OnePlus 7 Pro will get Android updates later this year or in early 2020 also, but the OnePlus 7T will have it first. It will showcase some of Google (And OnePlus') latest technology and software changes, and be the best and most refined version of their Oxygen OS 10 we've seen. The 7 Pro just got the OTA update, and the 7T is up next.
You'll want to wait for the OnePlus 7T Pro if you haven't already bought a phone yet in 2019.