He uses a flank-heavy formation so I wouldn't gamble in a flank attack formation such as 4-5-1 V.

Your opponent plays in a kind-of 3-4-3 diamond. The counter for 3-4-3 flat is 4-2-2-2 hexagon, so I would rather go for a 4-1(DMC)-3W-2 with mixed or through the middle attacking or a 4-1-4-1. Is he around the same level as you?