You don't necessarily need to specifically optimize for it: just do your development on a slower machine. If you're using a compiled language, you can offload c

You don't necessarily need to specifically optimize for it: just do your development on a slower machine. If you're using a compiled language, you can offload compilation with something like distcc for productivity's sake, but all your testing should be on the slow machine. It'll be pretty clear if some change you've made is going to impact people on older hardware, because you'll notice the moment you make the change. And if it's unbearably slow for you, it will be for a good chunk of your users as well.