Had the pleasure of flying the corridors for 14 years in the 1-11. I am pretty sure that in fact they were 10 statute miles wide either side of the centre line due to some quirk when being set up.
The upper level was FL100 and was assigned as per quadrantal rules meaning the centre and northern corridors were FL045, 065 and 085 outbound and 035, 055, 075 and 095 inbound. The south, haaving a track less than 270 degrees was 100 etc. outbound and 090 etc. inbound. The only exception was when the East Germans/Russians were having an exercise on Luneburg Heath when it would suddenly be OK to transit at 150 or 160!
It was possible to deviate outside the corridors if there were cunimbs blocking them so long as a full Pan call was made. PanAm was particularly good and precise at this and several times I heard the call, "Pan Pan, Pan Pan, Pan Pan - Clipper xxx, heavy weather on the left hand side, diverting x miles to the left/right of the corridor boundary". Never any repercussions that I knew of.
However the ATC was run by the US military and was a training base and they got extremely excited if you went within a mile or so of the edge, giving imidiate turn instructions. On the so called "Super 1-11" we had a wonderful area nav aid called Harco (based on Decca) and when working correctly we could navigate to within a few hundred metres of the boundaries. The main problem was that Harco would often "jump" a lane without warning so you had to be pretty bold to resist the frantic ATC instructions and convinced of your position.
It wasn't uncommon to be asked not to reply to calls from ATC for training purposes and to then see how long it took for the u/t controller to catch on - not long usually to their credit. Also when operating into THF they liked us to do "no gyro" PAR approaches - they too usually worked out well.
As far as speed was concerned we tried to fly the 1-11 "on the bell" at 333 kts, the vno. However the 727-100 did something in the order of 390kts so in the southern corridor which was much longer than the other two, if we got established at FL100 Pan Am would barrel past us at frequent intervals 2,000' below.
Happy days!