FSX add-on scenery question...?

I'm considering purchasing some terrain mesh sceneries from FSGenesis, specifically the 10m resolution package for the entire USA and the 76m World package. I seem to recall reading somewhere that FSX always defaults to the higher res scenery installed, so my question is this... If I have both the FSGenesis USA and world sceneries installed will I still get the benefit of the higher resolution mesh scenery when flying in the USA...?? Most of my flying is done in the US, but I might like to fly in other countries and regions of the world on occasion, and it would be nice to have some better quality scenery than the default for those times, so having the FSGenesis world scenery package seems to be a good way to accomplish that at a relatively low cost.