Internet sharing - effect on broadband speed

My iMac is placed in a garden office where my wifi signal barely reaches, so I use powerline adapters. These work superbly well but, in order to use an iPad or iPhone in the office, I have set my iMac to provide internet sharing via wifi (in effect, using the imac as a wifi repeater). This again works well but does anyone know if this degrades the broadband speed that I get on my iMac? I recently upgraded from ADSL to fibre broadband but I haven't noticed much difference when using the iMac.