Mixed bag there for sure. Some of the routes are VERY hard for the grade, some easy. In the original guidebook, there was a 5.8 mantle route on King on the Throne, for instance. It's been up graded to 5.12a... And, gym climbing is an interesting gage of "things". At the higher levels, on the steep sport climbs at the City, gym climbing and ratings really do cross over well. You can climb 5.11 in the gym, you'll fair well on She's the Bosch for instance. But, at the lower grades, especially given the style of climbing, gym v City of Rocks doesn't translate well. So much more subtle foot intensive movement than steep jugs. With the exception of a few of KP's super popular routes, most routes are under bolted or require a fair bit of gear to safely protect, or, aren't safely protected. This month's Climbing magazine has fun article about the City. Worth a read if you like the area. I even have a few off the radar route selections listed...(Reach the Sky used to be 5.9...soft grades...ha ha).