Hi John,
Trust me your probably in for a shock the first time the roads are white! BMW`s are great but they are useless in the lightest of snow . If you have never bought "winter tyres" then IMO do yourself a huge favour & buy some. You can run them all year round if you buy quality tyres. Ive run Continental winter tyres for the last 2 years & they have lasted over 20,000 miles. If the 5 series is the same as the 3 series then it will ride MUCH better on normal tyres as Run flats ruin the ride! The Continentals are fine in the summer ..unless your name is Lewis Hamilton... & in snow my 330d moves without much drama! They are fine in the wet on motorways & if your sticking to err hem the speed limits then you wont have any issues running them all year round! I will be fitting them to my 330Ci soon as last year it was an ornament in bad weather! Couldn't get it off the drive in snow last year but the 330d just drove off ..no worries! You don't mention if you live in town or rural areas or miles to work on what roads. They wont perform miracles in a muddy field (mind ive never tried lol) & although you can move off easily , stopping the bugga can still get interesting! Still far easier than with summer tyres.
Don't take my word for it, Read Auto express Finland winter tyre tests. Also find on you tube a BMW M3 on Nokian winter tyres walk away from a Ford KA (FWD) & a Subaru 4wd up hill in the fresh snow then later compacted snow.
This is my opinion & like you I didn't see the need to buy them. If you fit them, then enjoy laughing at EVERY Bmw you pass that's stuck !!!!!!!!!!
I hope this helps you mate.