Don't try that 800 strategy. The best 800 performances are nearly always run as a positive split (second lap slower than the first). You won't be able to pick it up every 100 on the last lap unless you ran the first lap very comfortably.
I've seen different formulas out there for the 800, one is the 10% rule:
Take 10% of your fastest 400. If your 400 PR is 60 seconds, add 10% (6 seconds) and you have a 66 second first lap. Then, add 10% of the first lap 6.6 seconds) to get a second lap of 72.6. Add them together and you get 2:18.
Another "rule" is that each lap can be looked at as a percentage of your best 400. I don't remember the percentages completely, but it's something like 92% 1st lap and 89% 2nd lap.
It's not a perfect formula and everyone is different, but the top 800 runners I coached ran times very close to each of these formulas.