well as an MD/PhD you want to have a research career (and you have about 3-7 interviews during the day so they can make sure you are set on academia). As you know, research careers are not as lucrative as a clinical career. However, the biggest advantage is that, if you are highly certain that you want to be in academia, you will not have to deal with an ounce of debt (maybe you can even save up money) compared to MD doing academia.
my PI is also a MSTP graduate from WashU within the last 10-12 years and did his derm residency at an Ivy league institution in CT. I think when he started around a 150k stipend when he got his first real job (and I think at that point had a K award). Most of that comes from his clinical department. He has no problems living comfortably, and has more money now. Our lab his 2 R01s, everyone has written their own grants and works pretty well. I'm pretty sure he has broken the 200k per year mark now with 0 debt to pay back (which is a huge deal). He spends 4.5 days "in" the lab, 0.5 days in the clinic seeing patients like he wants to (which is a huge deal). He repeatedly gets offers from other bigger/prestigious academic institutions since he is productive and also from private clinics starting at 350-500k a year hovering around the mean of 400k (he doesn't look at those).
The PhD doesn't influence how much money you make once you are starting your career. However, if will get you to a faculty position faster. It will make you more attractive towards the residency spots in competitive areas and prestigious institutions. Most people aim at a "fast-track" research residency, either in IM (3 years clinic, 3 years research) or others (like 2+2 derm). So hopefully you can end up where you want to and have a greater control of your career.
In terms of a research career, go MD/PhD over PhD alone since you will really only spend 2/3 more years in it and get a lot more out of it.
If you want to make the big money quick, go MD and a state school to minimize debt.
As far as me, I am in a top30 institution (public school out of my home state). My stats are 3.8/3.85sci and 38 MCAT (14/12/12/N - no one gives a shyt about the science section). You want to go to a place where you can have the best training in your research interest (if you know it). I applied to 30 schools, interviewed at 27. Decided to no longer be in ny/philly since the cost of living there was just too much. Undergrad at columbia - graduated in 3 years doing math/chem - and did research for 2 years after that to see if the field was for me (which you almost need to do to get in nowadays). I did not buy a property with my MSTP stipend, even though that was the goal (market fluctuated too much and I was in a relationship that could have possible ended up in me settling down).
The average stats at our institutional MSTP is 3.8+/35ish (that is interviewed and accepted). Of course the range varies and shyt.