For us to say anything meaningful, you should tell us at least whether you ride on flat or hilly roads, and how far, and in what style. Also tell us if you will install the motor yourself or have it done by the vendor or your bike shop; there are posters here with experience of both models. I give you a general answer including some more things for you to think about before you blow a thousand pounds.
The Cytronex is over twice the price of a much better specified system with front wheel drive I fitted, and it not only does not offer any reason for being so expensive, it will be painful in use by most enthusiastic cyclists. See
http://coolmainpress.com/BICYCLINGbuildingpedelec1.htmlThe concentration on light weight is simply foolish. There is no generally capable electric bike installation that is not
heavy. Lightweight installations disproportionately punish the owner by having to lug still substantial weight with very restricted range from a small battery, and a motor that will burn out sooner than you would expect. If you're building an electric bike for health reasons, I suggest you give up the Cytronex idea right here. If you're generally fit, read on.
Your question about torque is relevant but there is something even more important, which for shorthand I call Coulombs, like Jeremy Clarkson on Top Gear speaks of "torques". Basically a coulomb is a unit of electrical power delivered in a very short period of time, normally taken as one second. Practically, at every point in your ride, it doesn't matter how much total power is left in your battery, but how much it can deliver instantly when you need it, say if the hill steepens or you run out of puff near the top. In this regard, big batteries are more useful, because they can deliver more coulombs, i.e. more watts of power in the next second. The current Rolls-Royce built by BMW doesn't have a rev counter but a "Power Meter" which show instantly available power, on the same concept as your query about torque and my concept of coulombs.
The Cytronex marketers try to hide their inadequate battery by not telling you the rating in the normal form of Amp-hours, instead trying to bulldust you with the big-sounding "180Wh". That's only 5Ah. Amps measure real accelerative power, and is a good stand-in for torque, which electric motor makers often do not publish. On the Cytronex with that limp battery, I would not expect torque to be, at a guess, more than 35Nm.
On my first electric motor, the bottle battery was 9Ah and on my current mid-motor installation (not on a Thorn), the battery is, from memory, 14Ah. Both were/are adequate for my rides up to 25km in very hilly West Cork. I imagine the bigger battery would be okay to 40-50km but never went that far without recharging at a cafe or pub where we stopped. My batteries, with constant considerate care, are both going strong after many years of use. Even with obsessive care, I think that a 5Ah battery will be so heavily stressed all the time (that is, run close to its margins, which lithium batteries hate) that its life will be shortened. Since the battery is the most expensive part of the electric of a bike, it hurts only once to get the right size (to decide which we need the information in the first par), as opposed to getting a too-small battery which will hurt almost constantly by being inadequate in both distance and service life. It might surprise you to learn that the motor by itself in the above linked setup was less than £60 FOB China out of a total of £425 for an utterly complete kit delivered to my door by a British based dealer with excellent service.
