The OnePlus 3T is a phone that is really a near clone of the OnePlus 3 but with the Qualcomm Snapdragon 821 / Quad-core Kyro CPU vs the Snapdragon 820 on the previous one. The main improvement is that the 821 chip is able to run at full speed without overheating the phone and force a throttle down. Another improvement is a 3400mAh battery instead of 3000mAh on its older brother.
For slow motion however the camera should be the near the performance as camera improvements are “Intelligent Pixel Technology” which reduces noise in low light, New Saphire coated lens with slightly enhanced electronic image stabilization. The front selfie camera however offers 16MP on the 3T vs the 8MP of the OnePlus 3 which should yield much more detail for these types of captures.