I rode there a couple of years back with a local riding club - it was amazing! We galloped down Queen Anne's Ride (I think it's called) for about a mile - and I'm not exaggerating, I've just measured it on google maps!
Is it the Lions ride you're thinking of doing?
Hi, im stabled up the road and ride there regulary. They put up lots of jumps for the sponsered ride and theres lots of choice in height. Its about 2 hours roughly. It does get busy though as its a very popular sponsered ride but its defo worth it.