Hi aytidagupta,
Thanks for sharing your profile with us!
I'll address your question about R3 / R4 applications first. Generally, we do not advise candidates to apply in those rounds unless they have a very specific reason for having waited that long, such as having recently been discharged from military service. Otherwise, most spots in incoming classes are already filled by then, and admissions committees (AdComs) are inclined to ask why candidates didn't complete their applications earlier in the year if they already knew they wanted to enroll in business school. You'll usually be better off applying to any school in R1 or R2.
Regarding your competitiveness for Top 20 US programs, the first thing to note is that your current GMAT score is lower than desired. Ideally you want to score at or above the average score for any given program's incoming class, which for the Top 20 programs generally translates to the 700-730 range. If you've already taken the GMAT 3 times, you'll want to ask yourself how much room for improvement is left. That being said, you did increase your score significantly in your 3rd sitting compared to the 1st and 2nd sittings, so you're the one who's best positioned to decide whether a 4th attempt is worth it.
Aside from your GMAT score, your other main challenge is to provide a clear, compelling narrative about your career arc -- where you've coming from, why business school now is the logical next step, and where you're heading. You don't have quite as much work experience as the majority of Top 20 applicants whom you'll be competing against do, and your past jobs have been somewhat scattered rather than highly focused (operations for a pharma consulting firm is very different from marketing for a travel start-up). Why did you switch from your first job to your second? Why do you want to switch again to a fairly different field (MBB consulting may have certain similarities to pharma consulting, but AdComs might ask why you left pharma consulting in the first place if that's what you now say you want to do)? What you want to avoid is giving AdComs the impression that you jump from one thing to the next without continuity or logic -- you want to convince them that the career moves you've made so far make sense and are somehow connected, and you want to convince them that you've gained skills and knowledge pre-MBA that will be transferrable to your post-MBA career. If you're open to deferring your applications for another year, you may be someone who really benefits from an additional year of work experience under your belt.
I hope that's helpful! If you'd like to chat more, feel free to reach out to us on
www.admissionado.com. Best of luck!
Doris