I never cut my borders ahead of time. I wait until the top is pieced then square the top. I measure through the middle of the quilt lenghthwise and cut the lengthwise border. Do the same for crosswise. To splice the border for the necessary length is a personal preference. It's certainly easier to cut borders on the crossgrain and splice as needed. Sometimes I do that, but I REALLY love the look of an unspliced border. I just hate the hassle of cutting those perfect long lengths on the long grain. I've found that if I splice, where to place the splice really makes a difference. You don't want to place it near the edge of quilt. Sometimes that means wasting a lot of fabric, and I'm thinking I could have been better off yardage-wise cutting on the lengthwise grain.