[sik68]

The steepest 1st gear ratio'd car I've ever been in is a stock Nissan 350Z.

350Z
3.794 ratio 1st gear
3.538 ratio final drive
= 13.42 multiplication

Putting around, 1st gear is over 1/2 way through the intersection...the owner thought it was tolerable but disliked it for every day driving.

I've also ridden in a 335i BMW

BMW 335i
3.08 ratio 1st gear
4.055 ratio final drive
= 12.49 multiplication

My friend took me for a joyride as he just tuned the car for an extra 80hp and 100tq, I actually felt that this car was geared very well for hard launches and acceleration. The short 1st was nice when it was time to wind it out.

Porsche 911 Carrera
3.82 ratio 1st gear
3.44 ratio final drive
= 13.14 multiplication

So looking at a 12.x:1, it is probably steep, but given that the some oem's run well into the 13 range, it's probably not too ridiculous. Maybe you can recall some manual cars you've driven to give an impression of what a certain ratio feels like.