I had a lovely ride down here- although to be honest, getting down from these hills isn't always the most relaxing! Although you have just climbed up these hills, grinding up at an average of under 10mph is very different from descending down them at 30mph+! Even with my dodgy descending skills, I can well appreciate how the pro-riders go so fast and that cars/motorbikes struggle to keep up with them - it is quite gratifying to catch up cars on descents. Of course, the downside is you wear out brake pads a lot quicker!
This is my Garmin data for my ride from the Tumble to Llangynidr - I didn't take it fast by any stretch of the imagination, but averaged around 20mph - twice as fast as the climb uphill! http://connect.garmin.com/activity/81723417
It was beautiful here too:
Unfortunately I ran out of video camera space ("oh no!" I hear you cry. Don't worry there are many more hills and much more raggedy breathing to enjoy!) so you don't get it all I'm afraid. Obviously climbing the bloody things too slow.
Garmin data here: http://connect.garmin.com/activity/81723404 - you can see a somewhat unlikely speed spurt at 17 minutes - there is a lovely little dip where you have a choice to either relax, or pedal as hard as you can to try and take some speed up the hill with you. I kind of half-heartedly did the latter - my legs needed a rest. This is where the video camera said "enough". Photos are here too: http://www.flickr.com/photos/100hillsforgeorge/sets/72157626733015620/
22 minutes is what Simon estimates you should take to do the ride and that is what it took me roughly.
Instead of riding to the next hill, I popped the car on the roof and we headed off. It was just a bit TOO far away!