Collection Advice Needed

[redfred]

I am presently considering a 'new' piece, the problem at the moment is I am not too sure 'what', I am thinking maybe a DRSD or 5512 but I am open to suggestions. To make this happen would mean trading or selling one of the watches I currently have, the problem is which one and what would you go for,cash would be added to the deal.
The collection with my thoughts-

From top left going clockwise-

1975 6263 - This is a keeper
1966 5513 gilt, with a beautiful perfect dial.
1966 1675 gilt, stunning a definite keeper.
1972 MK IV red sub, very nice
1985 16660 seadweller with one of the nicest Stardust dials ever.
2009 16600 seadweller, hung onto this as its almost NOS
1967 5513 metres first ex Andrew Shear so obviousely very nice.
1978 1665 MK 1 Ex Mike Wood and a stunner.

I value your advice so the problem is of the 6 I would let go which would you choose and more importantly what would you set your sights on replacing it with.