stapfam

Custom will be fine----If you need it. Most will be able to fit a stock frame from one of the many manufacturers that are about.

In fact- with the variations of build from one manufacturer to another- you may be spoilt on choice for standard bikes that will fit perfectly.

Gearing and most bikes can be had with low enough gearing to suit your Knees- but that also depends on the type of mountains you intend to Climb.

So if you were happy with your "Old" Lemond with certain gearing- then Look at a similar bike for fit and a triple for the knees- if they require them.

So in other words- too many variables to give a perfect answer. What makes you think a custom frame would be required? What type of terrain are you going to be riding on? and what sort of rides do you plan**********