Perhaps a dumb question, but how can I force dwarf fortress on one core, and make other processes stay off it on win7?
Beware that on most modern CPUs, this will *decrease* performance, unless you have a crazy over the top cooling rig. The adaptive clocking routines, to over-simplify things, depend on being able to "overclock" a key core, let it heat up, and then shift the hot core's task to a different idle one when it gets close to being a problem. This allows single-core tasks to run at a significantly higher clock rate than the chip could average over the whole surface simultaneously. Locking a task (such as DF) to a single core defeats this, and will result in lower net performance.
I would suspect that the OP may be running up against memory transfer limitations. DF needs to work with far more memory than can fit into the on-die caches; it's regularly sucking gigabytes of info in from main memory on a good-sized embark. Once you've filled the transfer pipe, it doesn't matter how much faster your CPU is, it can't suck any more data through the straw to work with.
If the OP is into overclocking, dropping back on the CPU clocks and pushing the memory clocks up may well help; or you may already be at the limit for your hardware. Note also that DF is far less tolerant of memory corruption than your typical shooter; I'd want a clean overnight benchmark at a given speed before trusting it to run DF, not just a few tens of minutes.
Toady is supposedly starting to look at 64-bit versions; this may have implications for memory management if it rolls out in the near future, but it's going to be difficult to judge exactly what. My *guess* is that it will allow larger forts without crashing, but no substantial performance changes; but things could get significantly better or even somewhat worse.