Ah but Chris, you're falling into that trap already that "air watts" is the same as motor watts - if you refer to the old Hoover uprights that use the actual wattage power of 300w and 410w, there are not air watts and if there was a way to find out what the air watts were these days with these old vacuums, they wouldn't be very much from the hose. Also don't forget that of the Hoover models you do mention, those are upright by design only. I can recall from my own Hoover Junior U1104 that the suction through the hose wasn't that good, and a bit better with the convertor on my older Junior U1012 upright.
As Benny pointed out, air watts only goes so far -it is pointless taking into account air watts where bagged vacuums are concerned anyway as the dust eventually clogs the bag and the suction is reduced. This also occurs as well with the Vax/cheap branded bagless vacs with the "regularly clean" filters for extra maintenance of power - air watts can't be trusted unless they have been put into a vacuum that offers constant suction all the time, and we all know what brand uses that as a heavy advertiser.
As you know not all vacuums are made the same - the Numatic has an excellent sealed suction system and likewise with Sebo, it depends on the actual way air flow is maintained as well as minimising air leakage through performance that produces the power, not just the motor alone.
Lastly, as the previous owner of an Argos Value bagged upright, they're good at what they are designed to do - but getting the bags and belts for it can be a complete nightmare! Getting drive belts off the high street was impossible. I don't like to shop for everything online but that's an issue you have to do because Argos eventually get rid of stock like consumables as well as running out on a daily or weekly basis. The bagged upright is fantastic value, but you do have to do a lot more assembly than the cheapest mass-brand bagged vacuum that Argos sell and because of its exclusivity, I often had to buy two packs of dust bags to keep me going. It was cheap to buy, but to maintain for a medium sized home with 3 people sharing, not really that cost effective. If the bags had been larger on capacity, then yes I could well have seen it as an economical purchase; thus the Panasonic upright that Argos sell is far more reliable, not just in terms of performance but for the fact that nationally and locally, there are far more widespread parts, bags and filters - as well as having a larger dust bag capacity.