end-user/IT support staff ratio's

There is NO fixed user to support staff ratio.

Every industry and company is different.

2 major factors are:

The cost of downtime.

The type of user.

If downtime is costly, such as in a sales center, you need to have enough staff to respond to the "nominal" daily peek level of support calls.

In an office where users can switch to other tasks, a 1 hour or even 1 day call backlog may be acceptable.

How sophisticated are your users?
Can you talk them through tasks over the phone?
Or, do you need to do the work yourself.

Any number that you come across is just a guide.

You and your management need to determine what metrics to track in order to evaluate your specific situation.

Another factor that can come into play:
Do you have "value-added" tasks that the support techs can work on when they are not directly supporting a user?

If so, you need to determine how much time should be devoted to these tasks.
Then, you can adjust staff level to achieve the desired productivity on the tasks.

Chas