From the '05 Handbook:
(a) Unobstructed Exit. Where the location permits a continuous and unobstructed way of exit travel, a single entrance to the working space shall be permitted.
(b) Extra Working Space. Where the depth of the working space is twice that required by 110.26(A)(1), a single entrance shall be permitted. It shall be located so that the distance from the equipment to the nearest edge of the entrance is not less than the minimum clear distance specified in Table 110.26(A)(1) for equipment operating at that voltage and in that condition.
With regards to (a):
As Greg said...door should be on your 'south' wall.
With regards to (b):
110.26 (A)(1) as long as there is a minimum of 3' from the gear to the nearest edge of the door, it will fly.
So, IMHO, a single egress on the 'south wall' in your scenario would be compliant. And, IF you double to (6'), and maintain a minimum of 3' from the gear to the door edge, that too would be compliant.
BTW, I do everything to avoid one door rooms; being involved in the 'design' stages (as EC) I always squeezed out a large broom closet for my gear. LOL
I can't copy/paste the Handbook pics here, but if you need them, call me and I'll fax it to you.