I have worked as a dispatcher. Sorry for being too lazy to cross check JAR-OPS and the OM-B, but thatīs the way I handled it:
Some airplanes have a maximum allowed XWC, whereas others have a "demonstrated" XWC, you find this usually in the OM-B or the AFM.
If you have a "demonstrated" XWC, you can exceed that one staying legal, but I never did it, because it just doesnīt sound like a good idea to me.
A limit is a limit and therefore mandatory; quite a no-brainer.
For the destination, destination alternates and enroute alternates you can disregards the gusts, thus just consider the main windspeed. For ETOPS enroute alternates you HAVE to stick to the gusts according JAR-OPS.
Remember that the METARs and TAFs give you true winds, whereas the RWY designation magnetic (sometimes makes the crucial difference!).
Even though the wording is "SHOULD be within limits", my understanding is, when the OM-B denotes a mandatory limit for the XWC that is ecxeeded by the mean wind in the forecast, I consider it closed for planning purposes (though it may be legal to do it).
There are other examples of things that JAR-OPS allows you that just donīt make sense to me (e.g. "adequate" vs "suitable").
Doing flight planning I always tried to stay on the conservative side rather than just exploring the edges of the legal frame.
Iīm just wrinting this out of memory, hope it helps anyway.