Pulling successive shots from Silvia

Using my thermocouple probe on the boiler, I pull my shots when the
Silvia's temp has cycled down to around 105 degrees C (221 F).
The probe is of course only reading from top of boiler, not the group
head, and the temp swings fast once I've pulled those first two shots.
So the probe can't tell me anything about group-head consistency. The
question is -- if we have friends around and we knock and retamp
quickly, how many coffees can we pull in succession -- four, or six
maybe -- while we're still likely to get good results?