I use both technoligies when watching movies at my TV. I use SVP to get 60 frames/sec then output it to TV via HDMI and my TV does 120 frames/sec. It gives best result comparing to SVP and TV FI separately.
I wonder do you use a 120 hz screen? or does your display interpolate at 120hz but displaying 60hz? I am asking because my Epson projector has hardware FI that seems to work that way (Epson isn't really clear about this though).
I assumed enabling FI on my projector would conflict (artifacts) with the already 'true' 60hz SVP frames my computer is feeding.
I am kinda suprised you use both