Translation of "Pinnacle" in Japanese

This is the crux of it, if I can reach that pinnacle.

ここが最大の難所(なんしょ)だぞ

He's unstoppable right now but the question is how long he can remain at the pinnacle of his career.

彼、今のところは飛ぶ鳥も落とす勢いだけれど、あの威勢いつまでもつのか、疑問だね。