I perfer to do a dig race over roll racing any day. However the attractive part about roll racing is in that it's harder to get caught. If you do a roll race, it lasts all of 10 seconds. If you do a dig race, it lasts for minutes. Not including packing the 100 cars that follow you into a near by parking lot.
Plus Dig racing on the street in 9 second cars or faster is fairly dangerous. Few years back, I saw two cars lose traction and almost hit each other and then when they corrected they almost went into the crowd.
As far as the fastest I've ever been in a car. I'd say probably 175-180. I have no interest in going any faster then 150/160 ever again though, on the street anyway.