A couple things don't sound right. Where did you get the overnight margin of 10K for that spread? It should be considerably lower. Who is your current futures broker that is requiring this margin?
Referring to your first post, keep in mind that NQ is essentially a proxy for the tech sector (Nasdaq 100) and ES represents the broad market (S&P 500). These two can diverge considerably (in magnitude of price movement) even though they are highly correlated (move in same direction). So this "pair" has more risk than you suggest.