Mike
If you take enough different ones then eventually they'll all start to run togehter and the fact that you took it previously shouldn't matter much - unless it was very recent. Check out JQ+, it has over 600 questions on 9 different
test so you are almost guaranteed not to remember the questions from one test to another. Also, Marcus' mock exams each have 60 questions and I dont think any of them are duplicated either.
Hope that helps
Dave