GMAT Strategy

Let me start off with some context to my question. I graduated from a top 5 US public university (bottom of the Top 30 overall US schools) three years ago. Unfortunately I graduated with only a 3.24 overall GPA with a double major in Economics and Political Science. For my MBA I'm planning on targeting schools in the top 15 (Stern, Ross, Johnson, Darden, Haas). The last one is probably a stretch. As the subject of my post suggests, my questions is should I consider retaking the GMAT?

I took the test yesterday and scored a satisfactory 720 (Q49, V40). However, I had a terrible nights sleep prior to the test and believe I didn't perform near my peak. I also started the quant section ~2 minutes late, which threw off my timing a bit. However, I believe I got slightly lucky with the quant subject matter. As for the verbal, none of it came easily. I was in a complete daze. In particular, my timing was terrible and I had no clarity in my thought. I believe the latter was due to my poor nights sleep.

Is it worth studying for another month and potentially bumping up my score ~20 points? My motivation for considering this is that my GPA is probably a bit on the low side for my target schools. The reason I'm torn is that my score is within the +-30 point error from my practice tests. Accordingly, it's not like this score is entirely unrepresentative of my ability. Yet I think I can do better given a good nights sleep.

I don't plan on applying for to schools for another year so I have time. I also believe I have decent work experience in a desirable industry (biotech) and have a relatively compelling reason for pursuing my MBA.

Should I consider retaking the GMAT? Or does the 720 already do enough to counteract my low GPA? One of the reasons for my thinking is the study described in the below-linked WSJ article. I think everybody has known about the low-challenge high-GPA phenomenon for years, but this brings the subject to the fore.

https://online.wsj.com/article/SB1000142 ... 77584.html

For reference, I've reproduced below the results of my practice tests over the past few months.

Kaplan CAT1: 610
Kaplan CAT2: 640
Kaplan CAT3: 630
Kaplan CAT4: 670
Kaplan CAT5: 640
Kaplan CAT6: 660
Kaplan CAT1: 720 (Repeat)
Kaplan CAT7: 730
Kaplan CAT8: 720
GMAT Prep1: 740 (Q48, V44) (took on 07/07/13)
GMAT Prep2: 740 (Q48, V42) (took on 07/20/13)

Thanks in advance to everyone for any advice!