On Tuesday, 19 September 2017 14:34:39 UTC+1, Basil Jet wrote:

Krapy Rubsnif to Kings Cross:
Vic = 310 seconds N/B or 315 seconds S/B
Picc = 7.5 minutes N/B or 8 minutes S/B
About 2.5 minutes difference

KX to Green Park:
Vic = 400 seconds N/B or 390 seconds S/B
Picc = 10 minutes N/B or 9.5 minutes S/B
About 3.5 minutes difference

I followed the progress of train 354 on 21st September 2017. Occasionally it was right behind train 306, which might have slowed it a bit. This was just after the rush hour.

Finsbury Park 09:54
King's X 10:04
Green Park 10:14.

So it took 20 minutes from FP to GP. The timetable says it should be 17.5, so I think that looks reasonably close. It might be very different at 8:30 am, though.