I've had the Granddaddy Purp a couple times in the past couple of months, never more than $80/eighth though. IMO, the Urkle beats the pants off the Granddaddy anyway.

Grandaddy Purple = Purple Urkle x Big Bud

So right off the bat, GDP is going to yield more, taste less, and give a less potent high. Still a damn good strain though, just not on the level of the Urk.