Glen, do you already have a set of winter wheels?
If not, I can dig up the official winter alloy wheels for the Mk5, or if you prefer, I'll look for some similar steels.
And for tyre sizes, probably one of the best websites for wheel and tyre conversions is this one: http://www.venommotorsports.com/library/tirewheelcalculator.asp Just enter your existing tyre and wheel sizes, and fiddle around with potential options, and it will show you all the differences for wheel revolutions, gearing etc. 
I do not...I don't have a Mk6 either (yet!)
I do have some 195/45/16 Pirelli Snowsports which have never left me stranded in snow, or given me problems in the ice over the last 3 or 4 years (accross both the Mk3 GTI and Fabia vRS)...in fact I have been known to leave them on when it gets a little warm, as you can slide the car around really easily with them on when it gets too warm for them!
I had Toyo SnowProx before the Pirellis.
I don't think I'd run steels...a 17" set of OEM 'nice' easy to clean wheels I can live with.
I had the Spowsports on BBS RXs when I run RXIIs for summer on the Golf, and them on the standard vRS wheels when I run BBS RXs for summer...so want the car to 'look' reasonable whilst still being able to be driven.
205/50/17s seem as close as you can get, diameter and revs/mile wise...so they seem a good option, but any official info would be appreciated, thanks!