If yours is like mine, the 265/70/17 SHOULD make your speedometer a bit more accurate. With my stock 265/65/17 tires, my GPS shows me about 1.5 - 2 MPH slower than my actual speed. The additional 1" diameter should resolve that.
Other than that, the LT designation may cause the ride to stiffen a bit as compared to a "P" tire due to the LT's heavier construction.