Like I have been saying for years (not because I'm guessing, but because I know), anybody in athletics who really wants to dope can do it and not get caught, if they go about it correctly, in most countries.
Given the cycling usually required with serious PED's, I don't know that we would see any better times than are currently represented by the present-day world records, if doping was unrestricted.
Of course we would see some anomalies of race-day stimulants, but a special category could be carved-out, with mandatory race-day tests for those compounds--but the more substantial stuff, the battle should just be declared lost. The systems that are required to be monitored are too disparate, too sovereign, and too complicated to be regulated meaningfully.
Open season should be officially declared, in acknowledgement of current reality, and only race-day testing for stimulants should remain, which could be conducted vastly more efficiently than any testing in the present regime.