Zeustiak, a Tick is how long a particular component of the engine takes to complete during a frame. The combined tick lengths will be how long a frame is.
Unreal Script in UE3 was 20 x slower than C++. I’ve heard that Blueprints, which are exported to a more optimial form of Unreal Script, are around 10 x slower than C++. I don’t know what upcoming speed gains for BPs are in 4.5, but it will still lag behind C++. BP AI will certainly be an area people will be looking to claw back performance from in the future.