According to the original post it is supposed to be reasonably quick.
I wonder how "Quick" is defined in this context. In my experience on a Core i7 DOSBox is somewhat usable to emulate first gen windows 9x games (designed for 486 and low-range Pentium 1). But please note that DOSBox can only use 1 core, so you are not taking advantage of most of the Core i7 performance features.

You really should first verify that the images work (by trying on a desktop computer). Also you should replace the images with the original ones after a unsuccessful try on the N900. These harddrive images are not read-only and they tend to get corrupted very easily in DOSBox. I have experienced that myself a lot of times when experimenting with DOSBox on the Desktop. (DOSBox is not designed for windows 9x, and has a LOT of issues when trying to do so)