I think 200 people probably rules out anywhere in Marple. The maximum for Mellor golf club function room is 110 according to their web site.
How about the Moorside Hotel in Disley. They can cater for that number I think, and it is quite 'posh'.
If you really want to go to town, try Lyme Hall. I went to a wedding reception there a few years back. Very impressive and the catering was superb.
Only others that come to mind are Edgeley Park (they can cater for up to 600) or the larger hotels on the A6, such as the Alma Lodge.