200psi from your machine will fill a bucket considerably faster or slower than 200psi from a different machine. Unless every single carpet cleaning machine in the world uses the same pump, pressure means diddly squat, it's all about flow rate
With respect to amtech, upholstery being dry "within half an hour" is a load of shyte. You don't even get upholstery
properly dry in that time with a really powerful truckmount and especially not with a CFR hand tool
First objective is deal with the soiling conditions present; guaranteeing a drying time is secondary to getting the cleaning done properly. Just my opinion mind you
You should be getting water out of your tool at somewhere near to the tank temperature, over a short-ish hose run, so something is not quite right. I would definitely try an '04 jet and try to keep the trigger pulled for longer bursts to keep the heat coming through.
Regarding the chairs, if you want to produce a superficial improvement with foam, fill ya boots! If you're afraid to take on such a job with your current extraction system, maybe it's time to think about updating your machinery if this kind of work is getting more regular? There's nothing worse than dreading a job, and it's usually because you think you're going to struggle with the present equipment you have.
However if this is a rare sized job it obviously isn't worth rushing out and spending £40k on a truckmount setup to do it
300 dining chairs - seat pad and back pad? With a team of 2 using your current kit you should be able to knock that out in one decent day's work (will be knackering though!). With a good methodical system, 40 chairs per hour should be achievable, but obviously depends on working conditions, soil levels & fabric etc.
From experience doing such jobs, I'd advise a few things to make the job go easier. First of all ensure you've got plenty of space to work in, and hopefully use a floor which doesn't need drop sheets otherwise you'll have a nightmare. If it's a carpeted area don't bother sheeting it, just whack a bonnet round it quickly after you've cleaned and they'll be eternally grateful for the "free" carpet clean
PResuming it's a function room ypou should have plenbty of space - clear all the tables to one long side of the room and put al lthe chairs at one short end. Plan a production line from one end of the room to the other, use a few tables to stand air movers on in the drying area.
Get your helper to first of all to pull out the most minging chairs and get them sprayed up and agitated first, allowing a good dwell, working down the the cleanest ones which just get a quick spray and brush then straight to extraction.
The first few jobs you do like this will be a learning curve but it's quite satisfying, just don't underprice yourself