I do alot of these jobs realy good earner, what I do is mix up either gg4 or tfr solution in one of those pump up garden sprayers from B&Q and wind out the nozzle on the end of the lance so that it is only holding on a couple of threads, in this position with the thing pumped up to full pressure you get a powerful jet rather than a fan spray.
I point this directly at the gutter and fascia and apply the solution, leave to soak for 10 mins then brush with vikan and no water, this softens everthing up, then I connect up to outside tap and rinse, they come up lovely.
I usualy only use pure water for glass rinse, this also works on conservatorys.
As for getting behind gutters I also posted on here some time ago for a long bristled brush, but have found that the vikan does do the job just.
The only thing I cant remove Is the grey type staining you find on old white gutters, but this hardly seems to matter to the customers as they are so impressed with how clean they come up.
You will find if you do one job in a street you are almost guranteed to get others wanting the job done aswell.
Drew.