I have the slx22 which I have taken a section off, so now about 18 foot. I also have an extreme 25 with extreme brushes.
I bought the extreme because I have tennis elbow and it's quite painful and naturally the extreme is very light to use.
Which would I buy if I had neither...
It depends on your round. For awkward windows above connies and for working at length, the Extreme is amazing. Also, forget how big and strong you are, with an Extreme and extreme brushes you will be much quicker. If you're big and strong, you'll be superman speed!!!
Because of my elbows I would ideally like a round of bungalows to wfp because it's less stressful on the shoulders (i'm 51). In that case I would use the slx 18. Closed shorter length, it feels more durable and I can use a radius sill brush on the end (my favourite brush).
So for an average round which would i buy, no contest, spend the extra money and get the Extreme.