I have the following metrics from mysql workbench

After I have set innodb-buffer-pool-size to 6G, according to this answer's query on how to determine the recommended size.

While the used buffer usage was between 87% and 93% before I did the change in my.cnf (running with default values) it dramatically decreased now, so I'm wondering if 6G was too much. Especially because the key efficiency was between 97% and 99% before the change, which has lost some percents now.

Should I bother more about key efficiency or buffer usage? Should I decrease the buffer usage again?

The server specs are

Intel® Xeon® E5-1650 v3 
Hexa-Core Haswell Hyper-Threading-Technologie
128 GB DDR4 ECC RAM
2 x 480 GB SATA 6 Gb/s Data Center Series SSD