Stocks volatility/correlation: a way to boost portfolio?

First: I do not want to change my investing strategy (VT buy & hold). But I would like to understand more about stocks volatility, correlation and (potential, theoretical) portfolio improvement. And maybe use it for my fun fund only.

As i was searching for ideas for my fun fund i compared QQQ vs XBI. According to M*:

The way i understand it:

  • QQQ and XBI had (almost) the same return (starting and ending point are together): positive correlation of 1 for the period?
  • XBI was more volatile than QQQ (more swings)

So case study over last 10y, investing at the very same moment:

  • Case A: invest every month 100 usd only in qqq
  • Case B: invest every month 100 uds only in xbi
  • Case C: invest every month 50 usd in qqq and 50 usd in xbi without rebalancing btw them
  • Case D: Case C but with rebalancing
    Is it correct to say that at the end, case D would have the best return and case A-B-C would have the same return?

So would it be in general beneficial (highest potential return, highest risk) to couple 2 sectors with the highest correlation but with very different volatiilty?

And what about to couple 2 sectors with the lowest correlation? For example Info Tech with Utilities:

Does this combination reduces the risk (more than it reduces the return)?

EDIT: choice xbi vs qqq was random / results are (i suppose) just luck; prospective it will not do it again.