ORIGINAL: yellowtigermoth
I used clearview demo and it's not smooth on my system
I'm surprised to hear that ClearView didn't run well on your PC. I have Real Flight G5.5, ClearView, FMS, and EasyFly 3 SE. I've found the flight physics on ClearView to be the most accurate of the bunch. ClearView doesn't have particularly demanding system requirements, however, and it should have run buttery-smooth on your PC.
I can't imagine you'd be unhappy with the Phoenix flight simulator. Folks seem really happy with it.