Hmm. I don't see any difference between having only ttf-freefont installed and having only gsfonts-x11. However, installing ttf-bitstream-vera gives a significant improvement; the fonts aren't aesthetically ideal, but at least the three vertical strokes of 'm' are consistently the same distance apart rather than the gaps being in a 2:1 ratio! Thanks for your help.

msttcorefonts turns out to actually go ahead and download the MS fonts for you with wget, so it's a pretty pain free way to get slightly better fonts if your ideology allows free-beer-but-not-modifiable fonts on your system...