I also started during the last century and had to endure my friends (and business school classmates - I'm a "bent arrow") racking up huge financial gains during the go-go '90's while I toiled in obscurity in a lab. I also had the disturbing circumstance of being called by recruiters fairly frequently with job offers (a result of the last company for which I worked before coming back to school). Talk about tough - friends with money; other friends who were finishing med school though we'd started together; babies (both as classmates and of my own); and offers of jobs with large salaries. It was enough to get my attention and make me question the wisdom (sanity?) of staying in. I also know that almost EVERYONE goes through this kind of calculus, and most stay in (though many will go on to private practice or leave medicine altogether in the end - which brings up the question of what one looks for in screening applicants, but that's a whole 'nother contentious thread).
Well, you don't go into a combined degree program to get rich. If you did, then throw in the towel NOW, no matter what stage of training you've completed. All I can say is that, while I could have made more money elsewhere and had what many would consider quite a fulfilling career, it wasn't for me. The combined degree has been a great ~decade (oof - that surely is a long haul) and has had far more ups than downs (the downs seem to cluster at the 4-5 year point). Although academic medicine is no bed of roses, it's all about picking one's poisons. If you don't "feel it," think hard before staying. If you're even moderately interested in the lab, think hard before leaving. It really is a great program for the right people.
Drinking, gambling and shady friends..... Well, having hobbies does help (for me it's kids, flying, boating/fishing, hunting). Definitely keeps me more, if not completely, sane.
Well, off to sign out some cases (surgical pathology is a blast - see, that's the geek in me that made the MSTP enjoyable).
Good luck with the decision. It's a tough one.