I would say you will need a very high end computer for what you want to do.

Look at my signature for my system specs. I can't use everything at their ultra high settings. Most of my settings a very high, but I have turned down/off some things that hit my frame rates pretty hard. With my system and my FSX settings I get good frame rates.

Even using Orbx FTX AU, REX2 and REX Overdrive, I still get good frame rates on my system.

Mark