Ive never used the clx, so cant comment,
All i can say is that you will be using the 18ft slx for most of your working day, on the average domestic, so get the lightest and most rgid.
Again i cant comment on the clx, but the slx really lasts, ive had mine for 2 yrs now and its still going strong.
When i used 17ft extels, they only lasted 6 months, so in reallity ive saved money.