They use the same processor as iMacs use mobile chipsets. So they are the same speed. Does this mean one or the other is faster? Of course not, but depending on RAM, graphics cards, etc. one may or may not come out ahead.
Yes, they use the same chipset and ram, but the iMac has a 3.5" hd which will make it win in write/read situations. Graphicswise, the MBP owns the iMac as already posted.