I've got a really wimpy Karcher (1010 or something, its tiny) and a foam lance from CYC that I've been using for several years. I do get foam, but not really thick, and then when I spray it off after about 5(ish) mins, it leaves the traffic film on...although it has softened it, cos a light finger wipe and it comes off, with no pressure.
Having had my car detailed a few times, my detailers set up (petrol powered jet wash) is much better - it gets rid of the traffic film also.
So, I've been looking at a new set-up. Was always set on Karcher, and was looking at the K4 series, but read this thread and saw Nilfisk recommended, and I've read that before, so looked into them. For about £50 more than the Karcher, I got the P150, which is meant to be really powerful. Cheaper on Amazon than Screwfix:
http://www.amazon.co.uk/Nilfisk-P150-2-10-X-TRA-Pressure/dp/B004OTOIYM/ref=sr_1_1?ie=UTF8&qid=1389732063&sr=8-1&keywords=nilfisk+p150
And I've just dropped over £60 at CYC for some stuff...including a new foam lance as the one I have is for Karcher!
http://www.cleanyourcar.co.uk/washing-and-drying/snow-foam-lance-various-fittings/prod_371.html
So I've spent a shed load on this. If it gives the results I want then it will be worth it! Hopefully try it at the weekend, but will have to be careful I don't take the paint off!