GREAT TOPIC!!!
keep in mind I am not a great climber... this is how it stacks up for me:
I climb comfortably at 5.9 sport and trad = NO FALLS (most of the time;)) ON TOP ROPE
I lead comfortably at 5.7 sport
lead comfortably on a known climb 5.6/5.7 trad
I can top rope a 5.10 cack with falls/not sport though
I have mostly followed or top roped cracks, that is my personal preference so I feel like I climb those better. Whoever said that if you can't lead what you can top rope, than you need to work on your mental game is exactly right, because it is my head, not the inability to do moves that is in my way as far as leading trad and sport at a higher level