It's a great question and one that highlights how hard it is to win the Olympics (and hence why it's so special) - so many elements need to line up including even your age and experience.
A first thought it was for me a no-brainer. I can't get the images of Ovett short stepping for 1300m of the 1977 World Cup in Dusseldorf before dropping the hammer with one of the greatest bursts of speed ever seen in an elite 1500m race and this makes me want to answer simply yes to both. In Dusseldorf he runs 26.4 seconds for the final 200m in a 3.34 race where he is smiling and waving up the home straight. It's a kick so devastating that Walker for the first and only time in his mighty career just stepped off the track with 120m to go. We can't be 100% sure but from the footage we can guess Ovett runs something in the vicinity of 12.8/12.9 from 1300-1400m. For me it's still his signature race and my favorite Ovett race of all time.
But on closer inspection of both races it gets closer and more interesting. In '76 Walker closes out his gold in 25.17 in a 3.39 race (and 37.8 for the last 300m) - significantly faster than Ovett but it's also a much slower race. He also is not waving around up that home straight with Van Damme breathing hard down his neck. It is though still a very impressive performance and is mightily fast in that final half lap. So the question is Ovett - who would not have been leading that race at any point until his kick which almost certainly he would not have launched from 300m out (because he never did), have had enough wheels to pass the imposing and powerful frame of Walker up the home straight. At this pace Ovett is not accelerating so viciously like he does in '77 so it's really a test of strength and I just don't know - we have seen recently how important it is to be at the front of a race when you are flat to the boards because it is hard to get around bodies (think Jakob v Jake in Eugene)
So at first I thought it was Ovett but I don't know man - Walker in 75 and 76 in particular was tough, real tough. I think Walker holds on because Ovett isn't experienced or battle hardened enough even in '77 to run the right tactical race he needs to beat JW here. That's a big call given how awesome Ovett looks especially in that one defining race in Dusseldorf but that's my gut feeling.
As for 1980 - it's also interesting because we are still talking 1977 Ovett. The spanner in the works here is Straub because Straub runs the one type of tactical run that let's just say, wasn't exactly Ovetts favorite (an even longer grinding run for home that starts 700m out). Again, is the 1977 version of Ovett strong enough to withstand 1min33 for the last 700m? (1.47.X pace) as he was in 1980 (because even though he was 3rd he was still very close) - hard to say! 1977 Ovett was still almost more of an 800m guy stepping up to the 1500m whereas in 1980 it was the other way around.
Full disclosure, Ovett is my favorite miler ever - probably my favorite distance runner ever but I think 1977 was a transition year for him (more to the 1500m) and even though he was devastating in that World Cup race, it was a certain style of race that worked perfectly for him there. He is more likely to win the 1976 race in terms of physical capability, but on the flip side as an inexperienced international miler the question is does he put himself in the right spot to vs an equally legendary guy in Walker. Gut feeling - I think the answer to both is "maybe not" and I can't believe I'm writing that given my first response was pretty much yes to both.