Twitch.tv bitrate question

When it is recommended to set the bitrate/buffer around 3400 for 720 @ 60fps or 1080 @ 30fps... what happens if I set my bitrate/buffer around 5000 or 6000? Will Twitch simply not utilize anything over 3400 or will setting the bitrate higher adversely affect the quality of my stream? I'm looking to stream mostly first person shooter footage at 1080p (if possible). I hear it's not worth trying for 1080p @ 60fps if you're not partnered with Twitch. I'm assuming it's about bandwidth allocation?

My internet speed is around 7.4 Mbs down and 1.4 Mbs up.

8 Gb RAM
i5-4670k @ 4.5
EVGA 760 SC
 


According to http://obsproject.com/estimator - my recommended settings is 720 or 1080 @3500 bit/buffer rate (max). My notation is in Megabytes, not megabits.

My question is am I doing the viewers with slower internet a favor by pickin 3000 vs 3500? I'm trying to understand the bit rate for both parties.