My problem is that I'm already researching. I have a poster session and paper due for a conference in December.

This is common! (I had presented some posters by the time I started grad school.) But I assume that you're switching schools, in which case your research will be interrupted. This process of getting into a project that your advisor is excited about is a good opportunity to get the groundwork you're missing, because soon you'll be expected to prioritize research over coursework even more.

Classmates will be primarily focused on coursework, which should definitely take priority over research.

At least in my field, this philosophy is pretty roundly rejected. It was even common to hear advice to first-years like, "If you're getting all As in coursework, you're not focusing enough on research."

I'm skipping an MS and going straight to PhD.

In the US, going straight into an MS/PhD is common (at least in my field). In most European countries, students have to start with an MS, and a PhD is a three year program with no coursework at all. I went straight from undergrad into a combined MS/PhD program, but because I'm following my advisor to the UK, I'm entering a PhD program that assumes a Master's degree background and has no coursework.