If I were you, I wouldn't rush to sit for my STEP 1. Trust me, having some clinical experience is really important when dealing with MCQs. It's all so clinically oriented and you can score A LOT better with some actual, tangible experience in real life medicine. I am in a 6-year program as well and sat for the exam in the beginning of fifth year, ended up with an awesome score and got a ton of electives.
My advice is to work really hard to understand the material you are taught in med school, invest in a year of quality clinical practice and then focus for your step. That way you will be done with the whole thing in 3-4 months and hopefully score great.
Best of luck!