Why is my 980 TI outperforming my 1080? - performance

Question

Trying to make sure my new computer is setup properly, and noticed that its GeForce 1080 GPU is significantly underperforming the 980TI on my old system (when running Tensorflow jobs). Since the systems differ in more than just GPU, I wrote a small benchmark to isolate GPU matrix multiplication performance in TensorFlow. The results confirm that the new GPU is significantly slower. I know this is something to do with the software installed, but I've checked the obvious things: same python3, same cudnn, same numpy. What could be causing this strange performance gap?
Benchmarking Script:
import tensorflow as tf
import time
sess = tf.Session()
A = tf.random_uniform((1000,1000))
for i in range(int(1e3)):
A = (tf.matmul(A,A))
cur_time = time.clock()
sess.run(A)
print(time.clock()-cur_time)
Old System (980 Ti):
I tensorflow/stream_executor/dso_loader.cc:128] successfully opened CUDA library libcublas.so locally
I tensorflow/stream_executor/dso_loader.cc:128] successfully opened CUDA library libcudnn.so locally
I tensorflow/stream_executor/dso_loader.cc:128] successfully opened CUDA library libcufft.so locally
I tensorflow/stream_executor/dso_loader.cc:128] successfully opened CUDA library libcuda.so.1 locally
I tensorflow/stream_executor/dso_loader.cc:128] successfully opened CUDA library libcurand.so locally
I tensorflow/stream_executor/cuda/cuda_gpu_executor.cc:937] successful NUMA node read from SysFS had negative value (-1), but there must be at least one NUMA node, so returning NUMA node zero
I tensorflow/core/common_runtime/gpu/gpu_device.cc:885] Found device 0 with properties:
name: GeForce GTX 980 Ti
major: 5 minor: 2 memoryClockRate (GHz) 1.19
pciBusID 0000:01:00.0
Total memory: 5.93GiB
Free memory: 5.39GiB
I tensorflow/core/common_runtime/gpu/gpu_device.cc:906] DMA: 0
I tensorflow/core/common_runtime/gpu/gpu_device.cc:916] 0: Y
I tensorflow/core/common_runtime/gpu/gpu_device.cc:975] Creating TensorFlow device (/gpu:0) -> (device: 0, name: GeForce GTX 980 Ti, pci bus id: 0000:01:00.0)
time elapsed: 0.81484
New System (1080):
I tensorflow/stream_executor/dso_loader.cc:128] successfully opened CUDA library libcublas.so locally
I tensorflow/stream_executor/dso_loader.cc:128] successfully opened CUDA library libcudnn.so locally
I tensorflow/stream_executor/dso_loader.cc:128] successfully opened CUDA library libcufft.so locally
I tensorflow/stream_executor/dso_loader.cc:128] successfully opened CUDA library libcuda.so.1 locally
I tensorflow/stream_executor/dso_loader.cc:128] successfully opened CUDA library libcurand.so locally
I tensorflow/core/common_runtime/gpu/gpu_device.cc:885] Found device 0 with properties:
name: GeForce GTX 1080
major: 6 minor: 1 memoryClockRate (GHz) 1.898
pciBusID 0000:03:00.0
Total memory: 7.92GiB
Free memory: 7.57GiB
I tensorflow/core/common_runtime/gpu/gpu_device.cc:906] DMA: 0
I tensorflow/core/common_runtime/gpu/gpu_device.cc:916] 0: Y
I tensorflow/core/common_runtime/gpu/gpu_device.cc:975] Creating TensorFlow device (/gpu:0) -> (device: 0, name: GeForce GTX 1080, pci bus id: 0000:03:00.0)
time elapsed: 1.2753620000000003