As Raz said it is possible to create an experience 9 unit but you must keep re-training and re-training. When you wittle your troops down to the say 10 9 chevron troops and you retrain them they dont lose their experience but simply the group average goes down. You then send this unit into battle and next time they have experience 9 you will proberably have 17 or 18. Re-train then wittle down to about 25 now. Re-train, fight 30 left. Re-train, fight 34 left. Re-train fight 37 left...

This will go on until you have a reet good unit.