I have a moderately old laptop, with an AMD Turion 64 X2 TL-50 processor and 438 MB RAM (after the graphics takes a fair old chunk it seems). I've currently got lubuntu 64-bit on it, and am not 100% happy with the performance. (Though I'm very pleased with the system in other respects). I'm wondering whether 32-bit GNU/Linux might use less RAM, and thus result in better performance.

Or should I be more focussed on other things if I'm looking to boost performance, like maybe the hard drive, or stopping the CPU throttling down (/proc/cpuinfo reports 800MHz)?

32

If you do video processing or mathy things, 64, to use the extra registers, but as you say it will use more RAM.

I've put my usual favourite for low-spec machines, Vector Linux Light, on it. Might not look as pretty as Lubuntu but it's running absolutely great, and using about 1/2 - 2/3 of the RAM 'baseload' (logged in, nothing but a terminal opened).