5% is definitely on the low side, atb least for most assiduous of the abusers.
Everybody seems to agree that cross country skiers had it first in 1987.
From what I gathered, about 20 amateurs died in Belgium and the netherlands in 88 and 89 from suspected EPO use.
In other words they were the guinea pigs.
When doctors more or less had mastered the doses and "proper" techniques, pros dove in, starting mostly in 1990.
The only pros I know of who died early on and were clearly taking EPO were OOSTERBOSCH - an excellent TT racer - and Draijier ( sorry for the spelling) whose wife asked for an autopsy ( he died at age 26).
It probably took some effort to master sufficient knowledge and one can assume first tests were made on one day races.
In 1990 I was injured and could follow the Giro d'Italia much more closely than normal. It's only many years later that I understood those events that baffled me so much at the time.
When I realized what had happened in 1990 at that Giro, I started thinking about earlier events and I had some suspicions on LeMond in 89 ( after all he had been hospitalized in 1987 and I thought maybe he was given EPO at the time), but considering his current fight against doping I have to rule that out.
Then of course there is Fignon's extraordinary 1989 successes which make him a good early EPO candidate. He litterally seemed to rise from the dead that year.
Clearly if Chiappucci had known about EPO in 1990, LeMond would never have won.
Obviously all pro teams must have awakened to EPO after Bugno's 1990 victory in the Giro and there were must likely several trials made that year in a number of teams and races, including the TdF, although not as disastrous as the TDM affair of 1991!
So my vote goes to Bugno for a GT, but not ruling out Fignon in 1989. Other astonishing performances surfaced in 1987 : JF Bernard beating Herrera at the Ventoux, Roche's wins. Therefore I keep an open mind