I'm definitely using the faster settings. Check these out, they are comparisons between test encodes and the lossless source file:
Slow Settings: http://screenshotcomparison.com/comparison/138305
Fast Settings: http://screenshotcomparison.com/comparison/138306
Slow Settings: http://screenshotcomparison.com/comparison/138307
Fast Settings: http://screenshotcomparison.com/comparison/138308
Slow Settings: http://screenshotcomparison.com/comparison/138309
Fast Settings: http://screenshotcomparison.com/comparison/138311
Slow Settings: http://screenshotcomparison.com/comparison/138314
Fast Settings: http://screenshotcomparison.com/comparison/138316
And the speed is almost double, meaning it would probably take 4-5 days on my computer with the slower settings.