This is interesting. To order tabs, you need to know what the label of the tab and content within represents for the user. It can be done in a card sorting session, where users put pieces of information into more meaningful chunks of information. It can be open, where no label of the information chunk is given and the user is free to order and group in any way they feel best. If it's a closed card sort, the label of the information chunk is predetermined. Like having labels of "About Us", "Start", "Products", "Our Values", "Investor Relations".
User will then be asked to place phone number, quarterly report, vision, support, yearly report, organization, vacancies and much more under each label. When this is done, with several users you get statistics to base your decision on. It is rare to ask about which order these tabs should be in, but I see no problem with it. In fact I think you ask the right question here. If you can's decide - let your users guide you.
There are numerous of card sorting tools available, both freeware and proprietary ones. One that I like is xSort for Mac. Also there is a good book on Card Sorting, which one can read if interested.