Hi Pete
The Sebo Duo is a great tool to have, and the Prochem Products even better. However, if I was buying new, I would seriously look at the EnviroDry (sp?) equivalents, but regardless of which you go for, I would srongly advise that you buy the soft and stiff brushes as well as the standard. Soft are used for most carpets.
I'm not familiar with the Extracta range, so can't comment, but I am aware of the company's excellent reputaion for quality of machine, performance and back up service.
If I was looking for the most performance from the smallest package, an option worthy of consideration is the Alltec Aqua 40 with all the upgrades. This will give you 2x3 stage vacs and 100psi. This will cost about £1600 They may even have a 135psi pump option. I don't know the weight of the machine.
My feelings are that the best agitation possible will significantly improve your workrate and quality of work, and this should be your first port of call.
Safe and happy cleaning

Ken