I just read a very post from Robert Puddy. I am adding a link to it below as it is the best answer I have seen to the age old question of long copy vs short copy. Robert seems to have it down to exactly what I do when confronted by a long sales letter; so I hope it applies to the majority of other people too. Making it very useful data
He says (quote)
We know people dont read long sales letters from start to finish…
Here is what they do (and why a good long sales letter works)
First they scan the headline and the first paragraph (so this should be your strongest reason for buying) .
Read the rest here http://robertpuddy.com/long-sales-letter-suck/