Hi - sorry for the delay, real life has been killing me the last few weeks. 😐

As suggested, I've gone back to my laptop and tried replacing the SDL DLLs that come with 0.63 (which was slow) with the ones that came with 0.61 (which was fast).

The result - DOSBox 0.63 is now very, very much faster on my laptop. With its default DLLs it takes up 98-100% processor time without even running a game, but only 7-8% processor time if I replace the DLLs. So it looks very much like it's SDL and not DOSBox which is the problem, although I've no idea why this should be. 😀

Regardless, DOSBox 0.63 seems happy enough using the old DLLs so I'll leave them in place for now. Cheers for all the help!