I also agree that VsX reliance on the margin over #2 makes VsX too volatile and benchmarking against #5 or #10 would be better.
The only problem is comparison between eras: #10 in goals (or points) is a very different thing in a 6-team league and a 32-team league, while one can argue that #1 and #2 would have been #1 and #2 no matter how many teams we have and the competition to become #1 and #2 is always the same.
In any case, here are the best 5 % leads over #10 in goals for several all-time great goalscorers
Ovechkin 63-61-52-52-50
Gretzky 85-85-59-48-48
Lemieux 85-47-46-29-28
Bossy 73-42-33-33-28
Brett Hull 91-67-60-24-12
Stamkos 67-46-38-32-30
Bure 61-55-48-30-11
Here are the best 5 % leads over #5 in goals
Ovechkin 51-43-40-39-38
Gretzky 70-67-33-27-19
Lemieux 67-37-35-15-4
Bossy 47-24-19-15-15
Brett Hull 76-52-33-10
Stamkos 58-26-21-16-10
Bure 38-34-15-13-0
So, we have 2 seasons by Gretzky (92 and 87 goals), one season by Lemieux (85 goals), one season by Brett Hull (86 goals) that are clearly better than Ovechkin's 65 goal season. So post-expansion (or post-Esposito) Ovechkin's 65-goal season is at best #5.
Then we have more seasons in the same league as Ovechkin's 65-goal season - the 60-goal season by Stamkos, Brett Hull's 2nd-best season (70 goals), Bossy's best season (69 goals), Bure's peak (58 goals from 1999/2000).
Looking at the numbers, the difference is not huge: e.g., in terms of the lead over #5, Stamkos is ahead of Ovechkin 58 to 51; if #5 is at 43 goals (as in 2007/08), this is a difference of 3 goals. Bure is similarly behind Ovechkin 38 to 51 - so that would be a 5-goal difference.
I would personally put Stamkos peak at even and all other seasons a step behind Ovechkin - it sort of feels that scoring in 1978/79 or 1991/92 was higher that in 2007/08, so if Bossy and Hull Jr (with his 2nd-best season) are barely ahead of Ovechkin 2007/08 in raw goals, adjusting for the scoring level they should be a step behind.
I will do comparison with Bobby Hull, Richard, Howe and Esposito next time.
One last thing to mention, and probably leads over #5 are the best illustration: even though Ovechkin did not peak as highly as Gretzky, Lemieux, and Brett Hull, his career value as a goalscorer is still higher - just look at how flat his goal-scoring arc is and for how long he stays close to his peak production. And that's not all - he has five more seasons with healthy leads over #5, something none of the players above has.