Welcome to BHQ, you will learn alot just from reading and asking questions on this site.
First off if this banshee is a 410, you should have no problem eating that 400ex for breakfast, lunch, and dinner. I'm no suspension expert but a 6 inch swinger would prob be way to much if your just trail riding, but you could always sell that.
As for the bike being reliable? IMHO banshee's are just as reliable as any other quad...I have personally seen banshee's run years and years with no rebuild needed, and still holding a good compression. I think with any machine it is how you take care of it.
Any pics of this banshee? list of parts?