Going to RF6.5 will use more resources on your computer if you compare then full graphics to full graphics. Phoenix I think is a little more oriented towards heli's since there are a LOT of them on there from a lot of different manufacturers. RF is more of a plane, but the helis are VERY close to being true. I like flying both as I have both, it just depends on what I'm wanting to fly.
But as Lee stated, if you treat it as a game, it does get boring. Online flight is fantastic if your internet can handle it. And also as stated, it's usually the other way around. I can bust out some Smack in the sim, but I'm the hover master in real life lmao.