A CDN can help depending on how many PoPs ( points of presence ) you setup and the location based on where most of your traffic comes from. With a good CDN comes a cost. As mentioned, a CDN will is best if the content is replicated on multiple servers in different locations. Not only the top 1% of your files but all your files. Then that data is synced based on when files change.

For the most part membership sites can get by with only seeding the top 1% of files or the latest releases.
There is still a cost to that.

Before going to the CDN route see if you can get your server faster .. more memory, tweaked mysql or php settings, faster CPUs. Sometimes a faster server will do the trick. Then if you still need a faster solution a CDN may work. Just keep in mind, if you have to spend an additional $1000 a month ( or more ) to make customers that represent $100 a month in memberships happier it may not be worth the investment.

I do now of a few CDN networks that are adult friendly. Drop me a note so I can ask you a few more detailed questions on traffic.

Steven