The answer depends upon what type of work you are getting into.
Just because you can type fast, doesn't mean you can write well. But writing fast does have the added benefits of allowing you to quickly lay down a rough draft, tweak the hell out of it, clean it up during editing, and publish the final piece. Also, if you are going to be writing for a fast-paced publication that requires you to submit a certain amount of articles per day, you would help yourself by being able to type faster.
Seeing as I write for both (I've previously written for Mashable, CMSWire, and others), I have managed to find a good blend. I can usually write 700 - 1,000 words in a rough draft in the span of 30 or so minutes (assuming I don't need to break out of my flow to do research/fact checking). But it could require an hour or two of editing and fact checking to make this blob of text into something presentable.
For more long-form content like editorials and essays, however, I usually take my time and pay more attention to the flow of the article. 487
It is especially important because you have to keep the reader engaged and captivate his/her attention for a longer timespan (which is critical for the plentiful amount of readers that have ADHD in my industry).
In the latter case, writing speed isn't as important. Creating a story that people will want to read is critical, though, and even when I can pump out an impressive 125+ words per minute, little of that helps with the basics of crafting a well-written article. It might help get ideas out of my head faster, giving me more time to rearrange things and produce a better product, but that can only take you but so far.
But you are a writer, right? You are always looking for ways to improve your writing. Improving your writing speed can improve your writing. So take it slow for now; build up your writing speed over time.
TL;DR: Writing speed helps immensely in certain situations, but crafting a well-written product, in the end, requires creativity and dedication — something writing speed can't compensate for. 487