Ovi's record will be more impressive by virtue of him actually doing it. The goals record is also the flashier and more celebrated one to break.
The assist record
would be more impressive easily because it probably stands as Gretzky's single most unassailable record given that he came incredibly close to pretty much lapping the rest of the field. But it's also clear that Crosby has absolutely no shot at coming anywhere close to breaking it so that kind of makes this whole discussion pointless.
I don't feel like doing the actual complicated math to forecast any of this with any degree of statistical validity (like actual extrapolations and analysis to come up with reasonable estimates for his future. I'm more than happy to eyeball it and "this feels OK to guess about" though), but just looking at his numbers for his career his assist/game figures have been falling off the last 4 years (4 years ago it was 0.77 assists per game. This year it's .57 and it was a smooth descent in between). But let's say for the sake of argument he could level off on that decline and produce what he's doing this year for the foreseeable future without slipping any more.
right now he needs 233 assists to pass Francis for 2nd on the list. If he continues at his current pace for the rest of the year, assuming he doesn't miss any games he would rack up about 47 assists (I'm giving him an extra one for rounding purposes) and he would then be 186 assists shy of passing Francis.
at 0.57 assists per game it would take him another 329 games to get those 186 assists. or just the tiniest sliver over 4 full seasons if he were to never miss a game. So basically he would have to play every game from now until the beginnings of his age 42 season with zero appreciable decline to get 2nd place. Sid has done well to not miss a game the last couple of years, but history suggests that's not something to bank on, nor can we expect him to fight off father time for nearly another half-decade.
If he finishes this season with 47 assists as I noted above he would be at 1,064 which would squeak him 1 past Steve Yzerman for 9th on the list. He'd be just 15 back of Oates and easily able to do that next season. Joe Thornton is 45 assists up on our hypothetical end point for this year so even if he declines going forward he can probably do that with 1 more good year or 2 years if he starts to slide. By that point Sid's 39 and he would still be 20-25 assists behind Paul Coffey for 6th. Maybe one more decent year at 40 gets him there but that might be the end of the line. Because Jagr is 20 assists up on Coffey's mark of 1,135. Bourque is 14 beyond that, and Messier another 25 past Bourque.
So by the time he's 40 He's going to be 40 to 45 assists shy of cracking the top 5 and the question becomes how much beyond 40 years old does he want to/can he play and how much does the gradual drag of time and injury lengthen that journey. And that doesn't even account for whether or not he wants to leave Pittsburgh as they slide towards a teardown/rebuild scenario that's going to limit the talent around him and suppress his assist opportunities even more than just time and durability alone.
Ultimately this is a lot of blather to ask if Crosby reaching a comfortable 6th on the all-time assist list is anywhere close to the cache and importance of Ovechkin claiming the all-time goals crown. The answer is obviously "no" just as it was when I started this post, which only leaves me to ask why I wasted all my time on that fiddly but rudimentary math and eyeballing exercise.