Try backtest with different leverage levels and costs of borrowing.
Leveraging Berkshire depends partly on the cost and your attitude toward risk.
I would like to note Buffett's long standing attitude toward Berkshire leveraging its stock purchases as well as his general advice on leveraging stock purchases. Then I will mention his partners early use of leverage for some balance:
Buffett has been happy going the slower but safer route and has routinely shunned leverage.
Other than a few special situations that involve arbitrage (the details escape me at the moment) Buffett has declined leveraging Berkshire's market positions by borrowing. He has leveraged his insurance float, which is a different situation, and there was an academic paper showing that over half of Berkshire's outperformance has come from this.
Buffett believes the great majority of the time he could juice up his earn with leverage but when the perhaps one in a hundred years series of calamities occurs, Berkshire will still be around and strong. (Say... there is a monster market drop and then Berkshire's insurance businesses take multiple and massive hits).
Basically:
Buffett never minded going slower but safer and that is his general advice.
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Buffett's partner Charlie Munger, who taught Buffett a thing or two and whose rationality Bill Gates praises highly, used large leverage when he was young, before hooking up with Buffett.
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I think most people would be advised to not leverage their long term stock investments because of the cost of borrowing and the added risk.
Of course the younger one is and the less he has, the more likely it is that cases could be made in special situations for leveraging, but most people will assess these situations incorrectly.
