The reason why no one posts their own individual setups is because not everyone has identical setups and what works for one person many not work for you. For example, my Setups would make your computer scream "HELP ME, I CAN'T BREATHE!".
On a side note, that Estimator is about as good as it gets, Streaming is all about trial and error.
Anyway, Twitch doesn't like users going above 3500-4000 bitrate. I don't know which server is closest to you but It might be wise to ping to that server and see what your upload rate is to the closest streaming server available to you. Your custom buffer size should probably stay UNCHECKED but if you don't mind a second or two delay, you can set your buffer to 1.5x-2x your Bitrate. It'll yield better quality.
You've got an i5 Sandybridge, so try using the Veryfast Preset. Check your Process % and your FPS, if you've got room, try the Faster setting and repeat the process.
Make sure CBR is CHECKED, CFR CHECKED. Downscale to 720P@60FPS with the Lanczos filter.
Other than that, there is not much we can help you with. There is the custom settings parameters but it is probably best that you research and see what does what. Custom Settings is more about fine tuning to your own specific streaming setup. Don't mess with it if you don't know what they do.
As said though, a lot of trial and error and just in general, testing.