I've never paid any attention to the fpm file size after lightmapping as I don't use it, but is it really that significant of a difference? I always assumed the lightmap was a separate file, and with all the issues I've had with it, especially slower performance, I've just gone with real time, which works just fine, mostly.
MAME Cab PC: i7
[email protected] (passmark 9945), 12GB RAM, Win 8.1/64, GeForce GTX645 (passmark 1898); Shiny new laptop: i7
[email protected] (passmark 8586), 16GB RAM, Win 8.1/64, GeForce GTX870M (passmark 3598); Old laptop:
[email protected], 8GB RAM, Win 7/64, Intel 3000 graphics