Top 10 easily. Top 5 is the question.
Ovie is the greatest player of his generation - had the highest peak, leads in points, easily in primary points, while having 50% more goals than any other player (that's not a typo). No player in history has ever had that kind of goal scoring dominance. Ovie also has more Harts than anyone else, more Pearson nominations than any other player, and by far more hardware than any other player (17 major awards to Crosby's 11, and that's generously counting the Smythe that Sid obviously didn't earn).
Setting the all-time NHL goals record in a low scoring era would essentially mean Ovie has lapped the field in goal scoring. He wouldn't just have to be better at it than Gretzky, he'd have to be way better. Like, ~ 30% better.
Outside Howe and Gretzky - and to a far lesser extent Orr and Lemieux - Ovechkin's resume stacks up nicely against all the players from the 40s, 50s, 60s, 70s, and 80s. The key difference is that Ovechkin was playing in an international league and competing with an exponentially larger talent pool, whereas the players from the older decades were only competing against players from one small country, which itself has subsequently doubled in size. If a player's separation from the pack in 1965 is comparable to a player's separation in modern years, there is a solid rational basis for giving the edge to the modern player.