This kind of synthetic test just won't tell you anything meaningful - projects are so much more complex than this.
Different patches in VSTi's can take different amounts of processor power, even subtle tweaks to effects can add or subtract processor time.
The best bet is to not worry until you reach the limit of the computer, then either adjust the ASIO buffer accordingly or bounce some of the tracks.
You'll spend valuable time trying to work out something that is irrelevant - why not spend that time writing some music? - and what if your test tells you you can only make songs to a certain complexity? - will you decide to only write songs that are that complex?