Gerd Müller is the only top goalscorer we can take seriously imo, Pele's record is hard to take serious due to the circumstances at the time and the opposition he scored against.
Same with Romario where he suddenly got 400+ goals in Brazil after age 30.
And then you had players like Daek,Bican, Puskas who padded most or all of their record in what most likely was a very poor local competition.
Which means all the great goalscorers outside of Müller got 500+ but not over 600.
Leo will probably have 400 after Christmas, its no unrealistic that he gets 350 more in the 8/10 years after that.
It will depend on other things to, such as injuries, other players performances, if Neymar arrive this summer then in the future the goalscoring will be more eqilibrated between him and Messi rather than Messi scoring 50% of all goals for Barcelona. Also his own motivation will be a factor, can he sustain his dedication to the sport over the course of his whole career?
He now has these goalscoring records in La liga that no footballer is likely to break in our lifetime:
Most goals scored in one season
50 could be improved
Most goals scored in one season home
35 will never be improved
Most goals scored in one season away
23 will most likely be improved before the end of this season
Most rounds scoring in one season home
16 will probably never be improved
Most rounds scoring in one season away
14 will most likely be improved before the end of this season
Most consecutive rounds scoring
19 could be improved
Most consecutive rounds scoring away
12 could be improved
Most hat-tricks scored in one season
8 will probably never be improved
And before the end of this season he will most probably get Ronaldos record of scoring in 27 matches, he only has to score in 3 of the remaing 9 rounds.