There's a table on the wiki (http://cookieclicker.wikia.com/wiki/Building
) that shows what someone has calculated as the best numbers of buildings to have. I guess the idea is that the payback time (ratio of price to CpS gain) should be about the same for all the buildings. This was probably made for v2 and accurate for v2.002 and v2.0034.
But the current beta (v2.0041) has a new building with a very powerful synergy, which changes things.
I've tried to find out the same kind of information for the beta, by measuring CpS before and after buying each building and comparing to the price. This is for late game, with all building upgrades and synergies purchased, as well as heavenly upgrades like starter kit and starter kitchen. Here's a rough building distribution that puts payback times within about 15% of each other.
419 wizard towers
350 alchemy labs
343 time machines
303 antimatter condensers
I also learned that the only way to accurately measure CpS differences is to turn off short numbers and write down a whole bunch of digits, and also not have century egg. Seriously, the change in ten seconds from century egg is comparable to buying one cursor or mine.