The different sub domains that mashable employees are typically linked to different CDN’s (Content Delivery Networks). The fact you are using one server to load different resources means you only really need one domain (without sub domains). It sounds to me like you are overcomplicating this.
However, if you are looking for a speed performance boost then you are heading down the right path. The W3 Total Cache plugin will offload your resources onto a CDN like Amazon S3 so your site loads faster. Amazon S3 is also typically a more cost effective solution than running your own network of servers to serve static content.
/mytwocents
