Good morning,
There is not a way to log the value for the TLS version and Cipher used outbound of the gateway without turning on SSL debugging. Please log an idea if you feel that you would like to see this in the product.
If you need to conform to specific versions and levels, you should modify the TLS version and Cipher suites through the HTTP Routing assertion -> Connection tab
Click on the Cipher Suites to limit them down:
Sincerely,
Stephen Hughes
Broadcom Support