As Paul said, the iterator has not been implemented to loop faster on a foundset and based on my benchmarking actually is not.
Servoy 7.4.2 introduces performance improvments when looping on thousand of records, this is why, Marco, your execution time dropped from 10 minutes to 3 minutes.
Marco looping on a foundset with a normal loop on 7.4.2 should not be slower then the iterator, have you already made this kind of test ?