I recently obtained 5 grams of allegedly 10x salvia divinorum extract (fully legal here). I do not however, have a scale.

So, I took the average amount of cannabis that I have seen smoked from a bowl in the past:

~150-250 mg bowls based off of gram sizes, estimating 250 mg in a large bowl, which lasted for 10 hits. Estimating a hit to be about 25 mg. I know this logic/math is flawed, but it's a really rough estimate.

So estimating a small/medium hit at 25 mg, and estimating based off of the size of 1 gram of salvia extract, I started with a dosage I estimated at 5-10 mg and moved up.

I can post full trip reports if requested, but here is an overview using the Shulgin scale:
For experiment 1, the est. ~5 mg was a +1 experience, threshold certainly reached.
Exp. 2 I used ~10 mg based off of the first experiment, +2 physically, but didn't really reach a +2 mentally.
Exp. 3 I used ~20 mg based off of prior estimates, and still barely had a +2.
Exp. 4 I used ~40 mg based off of prior estimates (which I was strongly doubting at this point), and had a mid +2. This filled up most of the bowl of my pipe, and took me ~4 hits in quick succession.

I feel like I may have troubles doing more (lighters+intoxication=bad). I had been led to believe salvia ODs were common, thus my cautiousness.

I believe my breathing and holding technique is okay and I know the salvia is getting burned, as it changed to become more powdery (the salvia extract was already close to black). What would be your assumptions/advice, nexus community? How would you advance? I plan to pack the pipe to maximum capacity and try to take it all down, but it will take ~7 hits I'd guess. Is this typical? Is my salvia really a lower x than it was marked, perhaps?

That'd be my guess.

It may actually be 10x, but you're not sensitized to it yet. It took me a long time to get to breakthrough effects but once I got there, it was very easy to find my way back.

Part of the problem might be your smoking technique.

I only have average lung capacity, and I’m able to easily inhale a 40mg dose in a single breath with room to spare. Also, if you’re taking 4 hits in quick succession, then you’re not giving the Salvinorin any time to absorb.

Ideally, inhale a full 40mg dose in a single breath, hold it in for 20 – 30 seconds, get comfortable (salvia gives you a brief window of normalcy before taking hold), and then see what happens.