My parents breed labs and the breed is quite intelligent - they wouldn't use them for sniffer dogs, guide dogs etc if they weren't. They are generally dependable and easy going (although all breeds have exceptions to the rule) and you tend to find the yellow and black labs are the more intelligent. The chocolate ones are the dopey ones (in my experience).
Working line labs are better suited to running than the show line ones, although my yellow show line will happily run for miles with me. I think it's a case of building them up slowly and carefully to ensure they have the fitness and endurance.
I currently have 3 labs and all of them stop at roads and wait for the command to continue, they will sit, lie down, etc at any distance on command. I have done a lot of clicker training with my dogs and have worked closely with some of the country's top clicker trainers and if a dog is taught how to use its brain early on and think for themselves to work out problems, breed plays a smaller role in intelligence. Obviously, some breeds are naturally more intelligent than others but they can all be taught.
One thing you may need to watch out for is them getting sore paws (any breed not just labs) if you do a lot of running on hard surfaces. You can get paw wax which does help and again building up the distance and speed gradually helps lots too.
