Dear Crash,
I'm sorry, but I never give direct advice to anybody on an issue involving the measurement of body dimensions and bike fit without being there myself. I must see for myself that the measurements are being taken properly and then after a decision is made regarding fit and riding position I would have to be able to observe the rider to determine if the changes made were appropriate. I have experienced too many times where riders have given me their inseam measurement only to find out that when I measured them that the number was quite different.
It may sound petty, but I would feel very guilty if I found that I had given incorrect advice. Fitting a bike is not an exact science, although it is pretty close. But the factors of individual body mechanics, bone structure, and flexibility can change any dimension of the bike dramatically.
That is why most of the posters that I have read when addressing issues such as this shy away from getting too specific and prefer to stick to generalities and advice for the person asking the question to further research for themselves.
Fitting your bike properly is one of the most important things you can do when you begin to get serious. Prevention of injury and learning proper technique early require a bike that fits well. Not to mention the enjoyment and comfort that can be realized.
However, I can give you some parameters to look at.
Is your inseam measurement correct? Cycling shorts on, back against a wall, non-carpeted floor to stand on, feet flat on the floor (without shoes), shoulder-width appart? I think the best thing to use is a clip board, put one edge against the wall and bring the top edge up until it firmly touches your crotch/pelvic bone: have a friend measure you from the top of the clip board to the floor (obviously). This to a certain degree simulates sitting on the seat and gives a good starting point.
Your meaurements indicate a 155-160mm crank length as a "starting point", that is why I asked if you meaurements are correct.
I am from the camp that believes that 2.5mm increment changes are not significant enough to warrant the spending of hard-earned cash. Think in 5mm increments.
Crank length is about matching the correct length crank to your body's proportions to insure good mechanics while pedalling and injury prevention. You shouldn't think about it as leverage, gearing takes care of that.
Also, if you feel pain, back off!! Pain is your body's way of telling you something is wrong.
You may get completely different advice from a bike shop tech, the only thing I can say about LBS's is that they want to stay in business and usually they only stock 170-175mm cranks for road bikes. Do the research, especially if you are going to race, it is your body. After getting a fit ask for a second opinion from another experienced rider. Bike clubs and organized group rides are good for this.
Sorry for the long-winded response.
Good luck.