Sorry for the short answer - but just lost the long, involved one TWICE now by accidentally clicking on one of these bloody adverts to the right.
Anyway - speed is pretty meaningless - depends on the diameter of the vein / artery / capillary and the blood flow rate.
Which is about 0.00007777 cubic metres per second (or "cumecs" - the SI unit of flow)
Compare this with the lower reaches of the amazon, which flows at a rate of some 120 000 cubic metres per second, yet the longitutinal 'flow' can be as little as a couple of kilometeres per hour. Why? Because it is so wide, an enormous volume of water takes a long time to pass by.
In your blood vessels, the flow varies with distance from the heart, vascular heirachy, and the diameter of the vessel itself, so "speed" becomes pretty meaningless.