If the FPS is anything like in the GT6 demo then it is definitely a problem. I saw very noticeable slowdown in the demo with big fps drops (felt like it went below 20) and it affects the gameplay, it can also give the feeling of having input lag. iRacing for me didn't seem smooth during gameplay unless it was well over 100fps. Its often more about consistancy and smoothness of the gameplay, when the console is struggling and the framerates drop you tend to notice it in the gameplay a lot.
It can't really be compared to a 24fps movie where it is consistant and includes a healthy dab of natural motion blur between the frames. Your screen may be able to only refresh 60 times per second but you can notice the gameplay effects of high/consistant framerates well beyond that.
It's hard to explain, but I've played games where 30fps looks smooth, where 45fps looks great just as i've played games that struggled to play well and didnt feel good at 60fps, iRacing and Simraceway in particular.