Hi,

You add mesh in tesame way that you add other scenery. This means that you can install it to a folder other than cfs2 and you then activate it using the add scenery area within CFS2 settings.

Therefore you will do no harm in adding any mesh that you want and then deactivate it if you find any problems with it.

However, to answer your question.
Mesh is made at different quality levels being the LOD setting. The default for the Pacific default scenery/ mesh is 9 or 8. Other parts of the world are much lower than that.

Most mesh created for any of the FS series are usually 9 so will have the same impart as in the default area. As you are getting 30ish fps currently this should not be affected much by new mesh.

The new meshes around are much better than the default stuff so download and enjoy! You can always remove it if you don't like it

I get lower fps than you and adding mesh hasn't had much effect. High detailed planes cause a much bigger impact to me as I'm sure you have found.

Hope this helps

Kev