The following question appeared out of the blue in #yii on Freenode in September 2014:
hi i have started working on yii framework... and other pople have been continuously telling me that its a bad decision and using yii will slow down the site and performance will not be good, better go for core php...any of your thoughts will be great help..cheers
There is no way to really answer the question because it depends so heavily on the specific application, the technologies involved and their deployment. Plenty of attempts have been made to benchmark different MVCs but the results are usually perfectly irrelevant to any given application. It would be a foolish mistake to think that data from, for example, TechEmpower's Web Framework Benchmarks would predict relative performance of your web site.