VS007 Aircraft change

Hi everyone,
Just a quick question, I'm flying out on the VS007 on the 2nd June, I was hoping for a 747 as it was when I last went in June but according to UC reservation its scheduled to be a 340-600.
Having looked at online booking it appears that up to the 18th May this route uses a 747 (although flight history shows a mixture of both) then it changes to a 340-600, is there any particular reason for this? I'm just trying to sort out in my head which seat to go for. I realise that aircraft can be substituted at anytime but does the VS007 normally operate with the 340-600 over the summer?
Hope that makes sense! Thanks [:D]
Marc
Just a quick question, I'm flying out on the VS007 on the 2nd June, I was hoping for a 747 as it was when I last went in June but according to UC reservation its scheduled to be a 340-600.
Having looked at online booking it appears that up to the 18th May this route uses a 747 (although flight history shows a mixture of both) then it changes to a 340-600, is there any particular reason for this? I'm just trying to sort out in my head which seat to go for. I realise that aircraft can be substituted at anytime but does the VS007 normally operate with the 340-600 over the summer?
Hope that makes sense! Thanks [:D]
Marc