Interesting. From my notes I now have the following variants for the 1953 farthings:
1 + A
1 + A VIP proof
1 + A matte proof
1 + B
2 + A
2 + A proof
2 + B
2 + B proof
2 + B matte proof
2 + ? VIP proof (the variant from this thread)
The £6,500 listing you mention supposedly included a 2 + B VIP proof, but I'm not sure if there are any features of the coin which would make it differ in any way from the usual 2 + B proof, so I'm not including that on the list above.
I don't know if matte proof variants exist for 1 + B and 2 + A. The 1 + A and 2 + B both sold through Heritage (https://www.ha.com/c/search-results.zx?N=790+231&Nty=1&Ntt=farthing+1953+matte+proof&ic10=ArchiveTab-071515).
Looks like I'm going to have my work cut out if I want to acquire all of these variants. 😧