@globalarbtrader One more possibility is to analyse the average profit per instrument versus the amount of margin that instrument uses. Thus a sort of "bang for your buck" analysis. Although my account is a lot smaller than yours I found that it made sense to reduce the portfolio weight of certain instruments to avoid them using too much of the total available margin. It is a bit more subtle approach than just reducing the overall gearing, as you suggest in the third bullet.
That is an interesting approach, although I'd be surprised if 'average profit per unit of margin' was statistically significant. I guess it comes down to the fact I'm not really margin constrained, since I'm running my account at a risk level below where that would happen. The margin constraint is artificial and comes from the fact I'm choosing not to have the entire capital at risk sitting in cash, but instead to have a little bit of extra leverage on my entire portfolio.
GAT