ive done many different extract strengths, and my strongest trip, that (like many others) caused me to break through was from 10x. ive done 40x 30x, 20, 10, 5 etc. 40 is strong as hell, but 20x from a real brand will definitely get you there (maybe you have a strange genetic tolerance to salvinorin a). theres a company called ecstasy that makes salvia, herbal cigarettes and other herbal supplies, you can buy there stuff online or at a head shop. definitely my favorite brand.
anyways...
i suggest a few things some that werent mentioned, do as many of them as you can:
1. use a torch lighter...from what ive read (and experienced) salvinorin A has a much higher burning or oxidation or whatever point than THC, so a torch lighter helps combust more of that salvinorin A out of there. it ALSO helps you snap the entire hit much faster and painlessly. it almost instantly dissapears.
2. be high on cannabis before you do salvia...or at least put some weed at the bottom of you bowl piece to plug the hole, and give you that little THC high that always boosts psychedelics for me. doing salvia high on marijuana DEFINITELY makes it more intense for me.
3. bong (this is a must-have for me). ive never broken through on salvia without a bong.
4. snap as much of the hit as you can, and make sure the bowl it filled pretty fat and that you have a decent sized bowl piece that can hold a nice sturdy hit.
5. hold it in until a few seconds before you cant breath anymore. usually i hold it in as long as i can and i end up coughing or laughing it out automatically as i start tripping.
6. INHALE THE SMOKE WHEN YOU RIP IT. none of this inhale the smoke but most of it stays in your mouth bull. YOU RIP the bong, you move the bong away, you take a DEEP BREATH to get alllllllll that smoke deep into your lungs, and HOLD (see #5).
good luck my friend.
p.s. i also heard (i forgot where though) that salvinorin a degrades in the plant over time through UV light rays, so try to keep it out of the sun. but i do not believe heat is a problem (it might even dry it up so you can fit more in a bowl)