The Cross isn't really a particularly functional movement. But if you are intent on training it this is what I will say. Practice it, and stop at discomfort to avoid PAIN. Discomfort is good it means you are applying effort. PAIN means you are about too or already have caused damage. Use your own good judgement. The cross is hard elbow soreness will occur thats life.
I do weighted muscle-ups rather than a cross much more functional.