You have 768/128 - which is burst speed i.e. max speed of "bulk transfer". Pay attention that it have nothing to do with latency which will be quite big in your case. Why ?
Since max upload is 10k => meaning 80kbps of data only. You are not using any type of QoS which cause control packets (SYN, FIN, ACK etc) travel thru the same queue along with data packets. While data packets tends to be big (up to MTU), control packets tends to be small (~64 bytes).
Mule doesn't care about latency (it counts bps) but web browser, ssh (and you) does - it's suddently "very slow".
Solution: either futher limit upload from mule or use some QoS with packet prioritization.
Btw: I think we should add this question to FAQ

It's not the first time it's ascked, and answer is not quite trivial.