That's something we learned and were able to see for ourselves in a recent class. Being tense is much slower. Relaxing your upper body allowed for demonstrably faster draw times.
I was previously in the 1.4-1.5s camp, but after solid instruction, I was able to "let go" and make two .84 runs at 7 yards in the A zone. They weren't perfect, but I made A's. Now, after lots of practice, I can make first round hit in the A around .95 consistently. Integrating that into drawing with movement is a whole different story.