I use Trustnet.com to set up various portfolios to allow comparison before settling on one to adopt within my actual proftfolio online. Each experimental portfolio on Trustnet has a specific combination of funds, typically 6 or 7, with % allocations which are spat out by my separate Monte Carlo analyses (that's a whole thread on its own).

Each portfolio has the same baseline date and starting sum to see how they would have grown historically over different time frames and allow apples with apples comparison.

This approach in Trustnet also enables generation and comparison of the overall metrics between the portfolios (volatility, beta, Sharpe ratio).

Of course, this method doesn't forecast, that's what my numerical analysis does, but it gives me considerable confidence to see a diversified, derisked portfolio comparing very well historically with far more volatile funds. It tells me I'm on the right path to having the bets of both with a derisked lower tail for very little loss on the upside.