Hi. I have an original watch, SS 42mm which I've never used for swimming. I'm curious if there is a benefit / difference between aluminium & SS options on the series 2 for serious swimmers? Obviously there is a big price difference, and I'm the UK so they have jumped quite a bit too. I'm swimming 4/5 times a week and doing 3.5km a swim. The weeks I do a 5th swim this is normally in open water. Definitely going for a series 2 but wondering if there is a better option for swimmers, leaving price to one side? Thanks in advance.