I don't really have any designated loops... if I do a planned ride, it's because I'm riding with someone else. If I'm out by myself I just go wherever my bike ends up pointing.
There are TONS of places to ride around the Denver area. Lookout Mountain/Lariat Loop is a good ride. I like the part where you ride along I-70 on the shoulder. Fun stuff!
As far as slowing me down... I don't think I'm all that fast... more like the energizer bunny... I just keep going and going and going.
That's a good thing, though, with the rides I've got planned for this summer.
Dunno what kind of distance you've been doing, but lemme know when you want to ride, we'll work something out!
I'm currently riding with 3 clubs plus the bike forums group when they have stuff scheduled, so I can find a ride pretty much any time... my biggest issue is getting to the rides, as I don't have a vehicle.
I've got a pretty epic-sounding ride scheduled for the 29th, out of Fort Collins. 62 miles, 4,000 feet or more of climbing. Should be a good challenge.