Groundspeed is one of the most popular Scruggs tune, and also one of the most challenging. The timing in the B section is syncopated, so listen to that section a lot before jumping in.
This arrangement of Groundspeed is sure to test your technical abilities (and hopefully make you better!). There's a lot of mixing styles in this arrangements, so be sure to practice your transitions slowly.
This arrangement of Groundspeed is a lower register example of how you could play behind a fiddle player's solo. There's a lot of space for forward rolls over the G chord.