You are right that walnut is softer. But all wood will dent, scratch etc. And given your current conditions with no kids and a non running dog any species you decide will be fine.

If price is a concern walnut may not be the best. But then again theres not too many natural dark species that arent expensive.

Are you going prefinish??

Another species options to consider that are naturally dark with different shade variations are most exotics.

i.e Ip� (brazilian walnut) Brazilian Cherry. Santos Mahogany. Teak. And theres more.

Thanks for the suggestions. My study is only around 170 sq. ft., and I'm prepared to go up to around $10 per sq. foot uninstalled. I'm definitely leaning heavily towards pre-finished, as I want to avoid the dust and downtime. I told the salesperson at the local flooring store that the subfloor was concrete, and he said that glued down engineered would be the best option - is that right?

I saw a lot of nice walnuts and exotics at the Armstrong website. Are there some other manufacturers you might suggest I look at? Thanks again!

Glue is a good option. Armstrong is a good brand. Other brands may have a more specific look you may like so i really cant say this brand over that brand. As long as you stay away from the big box stores i think you will be okay.

I say stay at about the same or close thickness flooring as your light Bamboo. So the transition won't be quite apparent. Having your study new flooring run a different direction or 45 degree could make it more indenpendent of the rooms. As for color, contrast is a good idea. Besides what "gregmills" mentioned, there are many dark stained oak, maple and hickory could work for the same purpose.