So, after a lot of experimentation, pulling out of hair, cursing of the developer, I finally managed to get a build of Bitcoin compiled under MSVC.
all optimizations are on including SSE2, LTCG and favouring of Intel64 (well hey, that’s my processor)
Performance difference? The two builds I made (namely 32 and 64 bit) are practically equal in terms of performance - however, their performance is not equal to the stock build currently available.
On my quad-core with the stock Windows binary available from bitcoin.org I get about 1700k hashes a second. With the builds I produced under MSVC I get 2500K a second. Anyone interested?