I gather from your question that you could financially afford either, you are just asking which is the better deal/strategy. IMO, all other things (namely history and condition being equal), you should buy the truck with the lowest mileage, even if you pay more (within reason). You do increase your risk above 100K miles because of things that we have all proven wear out...starter contacts, cooling components, headgaskets. The farther you go over 100K, the more those things begin to press on you to address, solely at your expense.
Example: I would pay $14K for a 100K mile 1997 truck before I would pay $9K for a 150K mile 1997 truck. Its worth $5K more to me to have two years of mileage at my driving rate and 50K less mileage wear on a truck. Just my .02c.