How do I speed up `drush test-run` (compared to the SimpleTest UI)?
Consider using "php scripts/run-tests.sh" instead of "drush run-test". The former supports parallel test execution which improves runtime (as long as you have multiple test-classes). Compare:

$ php scripts/run-tests.sh --url http://d45.l User
...
Test run duration: 11 min 45 sec
$ php scripts/run-tests.sh --url http://d45.l --concurrency 3 User
...
Test run duration: 4 min 13 sec
$ php scripts/run-tests.sh --url http://d45.l --concurrency 6 User
...
Test run duration: 3 min 7 sec