Generally speaking, the research opportunities for MD and MD/PhD are the same. There are no specific pay differences between MD and MD/PhD and it has more to do with rank (ie what level professor you are) and funding grants versus clinical time. The amount one gets to do research is entirely dependent on funding and how much that funding covers effort. Most junior faculty will have about 75% research time covered under grants (K, AHA career development grant, etc). When one obtains and R or R-equivalent, the effort on the grant (and thus research) by the PI is typically reduced to cover other direct costs, namely personnel to do more of the hands on aspects (technician, research assistant, research nurse, etc.) and thus to get oneself more research time, one needs more funding. In my experience, one needs about 2-3 R grants (as PI, co-PI) to get funding for about 75-80% research effort (though in today's world, if you have one R, you're doing pretty good). All other effort, must be made up through other activities, usually clinical, though people can have have administrative effort (usually minimal). The NIH has a salary cap of what how much a grant can pay, and the only way to really boost someone's salary is through clinical activities. Thus, I have never seen people really try to reach high levels of effort on grants because you limit your salary. In general, most people will do about 50 to 70% research with the remaining clinical/administrative.
MD-only researcher aren't uncommon, though from a NIH-funding perspective, they are not as funded as MD/PhD. Most of this is likely due to effort though, MD-only K applicants have a lower submission and re-submission rate and thus funding rate, if I remember the data correctly. Again, MD and MD/PhD researchers have the same opportunities career-wise. The overall caveat is as mentioned above, time. The MD/PhD track is longer by several years. Prior to the days of reduced funding, this was offset by MD/PhD forgoing the prolonged times on K and going for Rs. Now everyone goes for K to R and thus the MD/PhD time is longer. That being said, MD-only candidates need some additional training time in residency or fellowship, either through T or F grants, and sometimes K12 and KL2. On the other hand, MD/PhD graduate medical school without debt, so there is no significant financial loss for the extra years of training.
Currently, I have about 75% research time, though that has been reduced recently due to the division being short staffed (this will always be true in that the clinical needs of the hospital/division will supersede ones research). I don't have a typical day, but I work about ~9 hour days in the lab (~50-60%, writing (papers, grants), ~20-30% doing experiments, ~10-20% meetings/clerical or somewhere thereabouts). Most of these days are done post-call (my calls are overnight in the hospital). I also do most of clinical time on the weekend (I typically work about 50% to 75% of the weekends per month to maximize time in the lab. I also write and read from home after my kids are asleep. As far as the right choice, I love research. Don't get me wrong, I enjoy clinical time too, but you don't really get to dream up ideas and test them in the clinical setting. You practice the standard of care which generally speaking has a path laid out. Additionally, and this is probably more personal, because we do so many things and offer treatments that really aren't based on science, but random association, and they don't offer cures. But we keep doing them because that's all we know and I find that frustrating. Granted, I don't think I'll invent the next thing since sliced bread, but I maybe I get to challenge a clinical concept with my science, or tackle things from a different angle and I find that very satisfying. And of course, if the NIH coffers dry up for whatever reason, I can always fall back on the MD part and just see patients and continue to make a living. As far as advice, sorry, I don't really have anything specific. I would just say take any and all research opportunities that you can. The more you experience it that better. And if you have that experience (which you should) were you do a project that you are excited about and you work hard, and it becomes a spectacular failure, but despite that, you really, really want to push on and find a new project to explore, you probably want to make research as a career.
