how many musicians per jam

[StuartR]

Assuming good gear and decent internet bandwidth ( 35 down, 5 up or better), would you expect expanding a jam from 4  to 5 members to tip us over the edge in terms of latency?

We're all within 70 miles of each other in the greater Seattle area.

It's not so much bandwidth as it is latency. If any of your 5 members have poor latency to any of your other session members then your audio timing will suffer. You can use the built-in statistics pane in the JK client session window to check each members latency to you. Just hover your mouse pointer over the little dot on each members rectangular display and look at the statistics. The little dot itself will be either green, yellow or red as a rough indication of latency, jitter etc.