Thanks for all of the feedback so far, everyone.
I absolutely know that I can do much better on IR, but the remainder of the exam? I really don't know. 740 was (just slightly) higher than any of my practice test scores, and while I do feel like I can continue to improve, I can appreciate that 740 is a very good score that is not easily replicated (much less exceeded) regardless of the level of preparation and ability of the individual test-taker. I would certainly like to think that I can get up to a 750 or 760 with a 7-8 IR (and a concomitant Quant boost), but that may all be wishful thinking on my part. (Any suggestions / advice on how to further raise Quant would be greatly appreciated, as I've worked my tail off on that end to date).
My concern here is basically this: I've expended an incredible amount of time and effort on this entire process, and my natural inclination is to not rest on my laurels now but to instead keep charging ahead and see where that takes me. Frankly, I have no idea how this entire process will ultimately play out, but the last thing I want is to get rejection letters in the mail in mid-December instead of acceptance letters when the latter reasonably could have be obtained had I just put in a bit more prep time and achieved even a marginal score increase.
Re: concerns of test prep and applications, I certainly can appreciate the concerns being voiced, but isn't that just unavoidable if I re-take the exam? I can certainly re-schedule my next GMAT until after the HBS deadline, but if I do that then I'm taking the exam days before the Stanford, Haas, and Kellogg Round 1 deadlines. I understand that doing all of this is going to be a massive time sink and require a tremendous amount of (additional) effort, but I just get the feeling that it will be that way with several of the applications, provided that I re-take. In general, I just see the only way of avoiding this prep v. applications conflict is if I just do not re-take the exam and instead begin working on the applications immediately. Am I just looking at this the wrong way?
And don't get me wrong, I understand that HBS (and most schools, frankly) is likely an extreme longshot, so perhaps it is foolish of me to even think in these terms of trying to further one specific application that is, in any event, unlikely to end in an acceptance letter. Even so, I hate to mail it in, figuratively speaking, when I could (at least in theory) submit a stronger application (and yes, I know that mindset is at least me being a bit stubborn, perhaps even to my own detriment). Again, I don't know how this ends for me, but I at least want it to end, for better or worse, with me at least having the peace of mind in knowing that I gave this process all that I possibly could have given it.
Also, random question on this front, can I submit my HBS application prior to the September 9th deadline with my current 740 score, and then after the Round 1 deadline supplement my application with an improved GMAT score from, say, an exam taken in mid-September? I would assume the answer to that would be no, but I don't know off-hand and I can't find anything definitive.
Any further thoughts/comments would be greatly appreciated.