Hi Pooty, welcome to SimV.
This has long been a problem with MSFS, aircraft are a little oversensitive to X-wind on the ground.
One way to "work-around" this is to play with your joystick sensitivites. I have mine set like this:

With the sensitivities set lower in the rudder axis, you'll find you don't "hunt" the centre line as much, and it's easier and more predictable to "kickout" of the crab before a X-wind touchdown. The only downside is that when in SLEW mode, it takes forever to spin your ship around, but I can live with that.
I think that the way the MSFS physics work, means that even if you plug in the right number for rudder area and the distance from the CG (moment arm), the rudder is much, much too powerful on most aircraft. Couple that with the adverse yaw you get (not present on most modern airliners due to the yaw-damper) and it's easy to get yourself into a 45 degree crab angle - not something you can easily do in real life!
Another suggestion - Have you tried some rudder pedals? I tried a set of CH rudder pedals at the UK FS show a few years back, and they made the world of difference to aircraft control. It's just "more natural" to do it with your feet.
Ric B.