How cool a matter of interest for me as well. I low alch with the explorer ring - but thats just because its free xp - but restricted to OSRS gold about 30 a day. However, I know there is a list of monsters and fall stats if you want to slay to get a stack of nats?
I train slayer and overlook that which critter had the best nat drops. . I know the roaches fall nats,but unless your into battling a lot then relying on this for nat production is mighty slow. On the plus side - the prices are extremely low on items today and runes are cheap to buy when you've got the gp to however a mighty stack. I have only played because 08 and I think this is the cheapest I've seen prices move. In the past I offered runes,but now I am burning them up as its not a big drop of money to use the runes I possess. At this time anyhow - Although things changes... And I really anticipate this latest dumb update to get figured out in our world. Until then im off to knock a few gold loose from the critters butt.
I've got similar stats, and I recently got a slayer mission for fire giants. So here is how I am fighting them: Lease - A sheet of food. A dragon dagger to special with every now and then. Glarial's amulet so that I can go in the waterfall to combat them. Fully billed games necklace to bank every now and then at the Barbarian Outpost.
Thus far, it is working really good and I just have to bank when I can't hold any more drops. You're seriously better off using a whip instead of Guthan's war spear. The damage per minute of the spear is awful, so only re-banking once you need to cheap RS gold is faster. Switch into a whip if you don't need to cure then. Easy to solve.