GMAT Strategy

Ok, I don't usually post to these things but I need to know if my goals are realistic or a pipe dream. I've only been studying for about a week now and I have taken the GMATPrep tests (2.5 times)...I only did the quant section the first time (kids were running around driving me crazy)! My goal is to score about 600 on the actual test (above the 50th percentile in each section). That may seem a liittle low compared to others on the board, but I'm trying to be realistic. I took the GMAT in 2004 and got a 530 after about 2 weeks of kind-of studying, but I was also a recent college grad. Now, I've been in the workforce and away from academics since 2004, so I'm a little worried. I have the official GMAT review guides (12th Edition & 2d Edition Quantitative Review) and multiple website resources. My weakness really seem to be in the quant section (probability, combinations, work problems and mixtures). I'm under a little bit of a time line that is work related so I'd like to test in about 30-40 days...is getting ~600ish a reasonable goal? I work 8-12/day, 5 days a week and have a wife +3 kids...so the time management part is on me.

Test version 1 (Quant Only)...31 Jan 11
Quant Score: 38
# Q's missed: -15

Test version 2...2 Feb 11
Quant: 44 (15 Q's missed)
Verbal: 38 (11 Q's missed)
Total: 670 (I'm just thinking I guesses a lot...this score just seems to high for me!)

Test version 1...6 Feb 11
Quant: 36 (17 Q's missed)
Verbal: 35 (11 Q's missed)
Total: 600

Thanks!

Mark