I haven't been on any of the tours you mention, but I would recommend having a scarf in your bag handy, and make sure you dress appropriately - ie long trousers for gents, shoes not sandals for gents and a long sleeved shirt for ladies. It's only common decency!

Have a wonderful time.

We went at the end of August with the Pope in residence and we both dressed accordingly even though it was in the high 80's.

Couldn't believe the amount of people wearing shorts etc, and they all got in without a problem. The only ones the Vatican mafia stopped were girls with bare shoulders.

Also photography was allowed.

Compare this with St Marks in Venice (or York Minster?) where there is a strict dress code and 'no photo!'.

Strangely you'll also find it strict round the corner in the Sistine Chapel.