Few days ago was reading Goran's interview where he was saying that now he is serving the fastest in his life, just due to technology change. So even if he peaked in this era his serve would be as big as everybody just whit much better placement. So thinking that his conditions would harm him or other big servers from from '90 big time is wrong
Speed guns perhaps, but Goran is still using the PC600. And I seriously doubt he's serving as fast, considering in 2006 or so he was serving around 10mph less on first serves.