I've found that .com/.net and .org domains all rank pretty similar. If the .com is already registered and the owner knows a little SEO it may be harder to outrank them, but it's really all based on who works on optimizing their site the best. I owned a .org and a .net and was able to outrank the .com, but that's because they had no clue about the most basic ways of optimizing their website. They had duplicate content, etc. I ranked first, they ranked 5th.
To answer your question, getting the .com is not going to make you rank faster than the .net.