I think the attack/str you get depends on who you want to fight, if you are interested in fighting more initiate and other rune pures then 75 attack would be good, but if you are more interested in fighting mains and tanks then 90+ attack doesn't hurt.
Like I said I've never made a berserker pure, but I think that 70/85/45 would be a good start, 85 strength and a whip is enough to hit quite high. 34 pray would be a solid start, but if you get to a higher level then getting 43 or even 52 isn't a bad idea, because of the amount of rushers/pjers.
I'd also be sure to get venge, that's one of the things that can seperate a good rune pure from a great rune pure.
And like I said before, be sure to get good gear (Barrows gloves/rune defender for pking, Fire cape/defender for doing mini games and such.) Gear will make you hit more accurate and higher like attack and strength do, but it's better in a way where it doesn't raise combat. A rune pure can be 99 strength, but if he has a combat brace and kite he won't max any higher then a 92 strength rune pure with barrows gloves/defender.
Good luck with whatever you decide to do.