The motor you linked to is 3000 RPM with a gear reduction of 9.778. The output shaft would be 307 RPM.
(3000 / 9.778 = 307)
Using the 9 tooth sprocket to your 40 tooth wheel sprocket will yield 69 RPM of the bike wheel.
(307 x 9/40 = 69)
On your bike that would be (69/160) or 43% of what you were pedaling. (4mph, or 6.6km/h)
Although you won't set any speed records, it will be amazing on hills. ]
If I were you, I would see if I can find a larger sprocket for the motor (~18-20 teeth) or a smaller one for the wheel (again ~18-20 teeth)
If you get this motor: 350W Motor - 24 Volts (Style: MY1016)
and chain it directly to your 40tooth rear wheel sprocket, you'd be looking at a wheel speed of 728 RPM (43mph, 70km/h). The speed might be great, but I would expect the motor to be severely bogged down. It might work with a larger motor(>500 Watt) but a 350 Watt just wouldn't have the juice to make it go. Also, the sprocket on that motor is a different pitch than a standard bike chain, so you would need either a different sprocket on the motor, or a double step-down like I used.
When I built my bike (in 2009) I thought long and hard about the simplest way to build it. I found this blog quite helpful: http://www.electricycle.com/