To elaborate: yes, MSTP = MD/PhD program that has a training grant from the NIH to fund specifically the training of MD/PhD students. MSTP = huge prestige for the parent institution, they have to resubmit the grant every 5 years, so it's important for current MSTPs to maintain excellent standards, two of which are average GPA and MCAT of matriculating students. Institutions can lose MSTP status, i.e. OHSU, so they take this very seriously. For the student, MSTP means guaranteed stipend during the entire duration of training as well as full tuition waiver. Some non-MSTP MD/PhD programs, especially those gunning for MSTP funding, provide the same financial perks as MSTPs, but not all. Some programs that are on the cusp are Penn St., BU, OHSU, and UMass.
Most of the time MD/PhD students take Step 1 during the same time that their MD counterparts take it, after M2. For the schools that have an 18-mo preclinical, it really depends on the program. For example, Columbia has their MD/PhD students take Step 1 before entering the PhD portion without doing any clinical rotations before.
MD students aren't really elite (except for Top 20.). Other than that, you're pretty much right. Many MSTP students have graduated from Ivy League undergrads or similar high-quality institutions... Yep, essentially invincible.
