Are you quilting this on a LA or Domestic Sewing machine? I have done all overs on T-shirt quilts and they look fine once they are all done. Prior to getting my LA I tied them every 3" ignoring the designs printed on the T-shirts and that looked fine as well. A big X through the shirt could probably look OK as long as you fulfill the minimum quilted spacing the batting requires. It is kind of hard to offer suggestions without seeing the quilt and knowing what you are working with.