So you have a performance specialization AND do full-stack web development. How do you position yourself in the market place?
For example, most of my work is also fullstack web-development, but I also know how to build highly-available systems with Erlang/Elixir, but I'm not sure how to squeeze the latter into the messaging.
Imagine having a toothpick, saw, wine opener, knife, and other various tools. Now put them all into the very first Swiss Army Knife and try explaining that to someone. Who are you going to explain it to? A carpenter who needs full size professional tools won't need that, but maybe a soldier in the Swiss Army looking for handy tools to cart around in the field would!
Figuring out who needs your services is the first challenge. Maybe high availability systems and full stack web development intersects where people need a front end that ties into a reliable backend (querying a database, visualizing a system, real time analysys, etc.) That's your target customer.
Does your target customer have a name for full stack plus high availability already? To make something up, let's call it Full StackOps. Sell them your Full StackOps wizardry. If target customer has a different name for Full StackOps, you'll have to try to figure out how to tailor your message per customer. If there's no name, try making one up!
Or just generate referral for yourself, so anytime customers need a Full StackOps-like person, their first thought is to call you.
Know your customer, and market the portion of your skills that's most relevant to them.
I would go so far as to have two separate blogs/websites if you're going to market skills as disparate as mine.