You won't type faster than you think. Typing fast - apart from the manual ability to do it - requires thinking fluently. Maybe you're inhibiting yourself by self-editing while you're forming the sentences in your mind as you're typing. Try free-writing: writing anything, as long as it's English (not random letters), not censoring anything, nonsense or sense welcome indifferently. What's the fastest you can write without putting on the brakes to judge? That would be the upper limit of your dexterity. (It's also a good exercise.)
Practice is a huge factor in dexterity. I think my typing speed increased linearly from the 40s to the 70-80 wpm range during the four years or so when time I was typing 3,000-10,000 words (10-20) pages every day. It has plateaued there for the last 10 years, because I just don't type as much.
Your gear counts. For me the ultimate feel was the IBM Selectric II, the one with the ball. The whirr and strike of when you hit a key, the hum of the machine waiting if you paused to ponder, encouraged typing. Most computer keyboards today make dispiriting noises. Hackers and writers will prefer the Das Keyboard (http://www.daskeyboard.com/). They say the all-black one forces your brain to touch type since it's hopeless to hunt and peck. I like it mostly because of the feel - the force you need to type on an 'a' or a semi-colong is less than for an "f" or a "j". The Das has a real smooth ride. There's something in that racket that encourages fast typing, like the first few pings of metallic raindrops building to a sustained mechanical storm - all because of your awesome creativity and work ethic. You can even pack and play - take it on trips for you if you know you will have to use someone else's inferior desktop setup.
The fastest way to write is steno. Plover (http://plover.stenoknight.com/) has been mentioned on HN recently.
Practice is the most important - Gladwell's annoying 10,000 hours and all. Not only rack up the hours, but practice with your whole body and mind. What are you writing, anyway? Don't think for a second that Malmsteen played guitar to meet a metric. You gotta have a feel for what, and why you're doing, what you're doing.
In summary like what you write, like your gear, and use it intensely. If you don't improve then you might be limited genetically, which doesn't matter. Once the ink dries, nobody knows how long it took you.