four months ago, I was pondering exactly the same question, and I opted for the speedster in the end. I upgraded the wand to the wonder wand, and I am very pleased with my purchase. In the end, the deciding factor for me was the cost, as the money I saved was enough to purchase an enviro-dri for aggitation. I felt that this would be money better spent, and has proved to be so....

As yet, I have not cleaned a carpet at 400 psi, and I can see no reason why I would need too... For carpets I vary the psi between 200 and 300 when using the WW, and when using a hand tool or cfr upholstery tool I keep the machine running at 200.
With regards to re-fills I have not really paid that much attention, but today I cleaned a lounge/diner, h/s/l and a downstairs toilet with only one re-fill.
Hope this helps
Regards
Paul