I can't reply to your other post - the page gives an error.
Here is my comment:
First - see p.91 of user guide. More details - it depends on whether you run P2V or V2V conversions (P2V means powered on sources, whether physical or virtual). For V2V the maximum is 20.
As for the impact - it depends even more on P2V/V2V. Data traffic passes through converter server in case of V2V; it flows from source machine to destination ESX in case of P2V.