Strength should remain same as attack (like you've set it, anat) as i found that Attack was far too easy to get 1.5m xp in. Were it possible to go back in time and change, should really be 2m for higher tier for it. Obviously though with strength you'd have to use a d scim or if you have the money, a godsword so therefore it needs to be more leniant. I'd say 1.5m is just fine

As for prayer, in my opinion the tiers are very low indeed :S The only source of getting prayer up isn't from buying the dragon bones on the GE and then using thing (Although that's what im doing w/ 45m of my money

>.<). It's slower but very cheap to just kill for your d bones. Doing a week of killing green dragons with a dragon scimitar (strength) could give you at least middle tier strength while giving the dragon bones for higher tier prayer tbh :S I'd suggest (Just suggestion <3 no need to take into account if feel differently)
Lower Tier: 50,000 - 150,000. Middle Tier: 150,000 - 425,000. Higher tier 425,000+
Just my opinion though

~Mugger84