Apologies, when I said "in guests" I meant only guests I was iper'fing.
To clarify: guests on different but virtually identical hosts - iperf3 between such guests.

What should a "typical" _tc_ look like with libvirt doing bandwidth management?
Seems that libvirt does QoS on the hosts - this is with a single net bandwidth'ed:

-> $ tc -s -d class show dev nm-bridge1011
class htb 1:1 root rate 4882Mbit ceil 4960Mbit linklayer ethernet burst 1601b/1mpu 0b cburst 1626b/1mpu 0b level 7 
 Sent 9559833379 bytes 10652255 pkt (dropped 0, overlimits 594941 requeues 0) 
 backlog 0b 0p requeues 0
 lended: 0 borrowed: 0 giants: 0
 tokens: 39 ctokens: 39

class htb 1:2 parent 1:1 leaf 2: prio 0 quantum 52083 rate 4882Mbit ceil 4960Mbit linklayer ethernet burst 1601b/1mpu 0b cburst 1626b/1mpu 0b level 0 
 Sent 9559833379 bytes 10652255 pkt (dropped 0, overlimits 641156 requeues 0) 
 backlog 0b 0p requeues 0
 lended: 10399228 borrowed: 0 giants: 0
 tokens: 39 ctokens: 39

and yet...
What might be not/happening here?
thanks, L.