Using golds would kill you- they're so slow. In a similiar vein, greens are very high gp/xp (around 20 gp/xp last time I calculated it, which was admittedly a long time ago). If I was in your position I'd slay for the charms, as slayer ranks are hot :^_^:. If you don't care for ranks, CT waterfiends can easily yield 150 crimsons/hr. Also regarding your idea to make steel titans when you achieve 99, titans are easy to buy on GE, as are the scrolls, and often buy for lowest. If you're going for ranks then by all means, but it's not really worth it to make them. Yaks are the better option (or were: like I said I did all my calculations quite a while ago). EDIT: Just read the last bit of your post! Steel titans are worth using on anything you can, really. I use them when I do fire giants, nechs, dust devils, dagannoths, m-bloodveld. Probably more which I can't recall right now. I use the scrolls on anything which I don't cannon.