OK so I got curious and went to the trouble of setting up the older system again.  Apparently the default intensity when zecminer runs is 6, on a scale of 0-9.  It gives the error msg that there is not enough GPU memory on both systems, and drops to 4. At which setting performance is awful.

But, on my previous system, I see that I had the intensity explicitly set to 3.  Setting it to 3 on both systems cranked up the speed to max, as far as I can tell.

This makes no sense to me, but it's what's working right now.

On a side note, for some reason Nicehash is running CryptoNight on my previous system, and Equihash (Claymore's zecminer) on this system (exact same GPUs, as noted previously.)  They have different speed CPU's, etc. so that might have something to do with it.

Sorry if this is discussed previously but can't find it.

I'm using zecminer via NiceHash, but I think that's irrelevant.  Last night the program switched to zecminer as the most profitable, but when the program ran, it reduced the intensity, thereby dropping the revenue by an order of magnitude.  (I noticed GPU temp was only 44C).  I verified this by running zecminer by hand.  When it starts, it says the graphics card doesn't have enough memory, so it reduces intensity to 4, rendering it pretty much a waste of time.  It makes no difference if the higher intensity is a default or if I specify it explicitly as a parameter value, it still gets dropped.  All recommended environment values appear to be set correctly.

Windows 10, AMD R9 270X, 2G, 15.2 driver

Is there a workaround for this?  I could take this msg at face value, but I could have sworn I ran this previously on a different computer with the exact same model card and it ran at high intensity.  (On second thought, I think that one was running the newest AMD drivers - wonder if that might make a difference?)

Thanks man.  I'm not sure what it was, but mine just jumped up to 250-300k range too.  What change do you think most contributed to that?  I imagine my intensity was off, but frankly I see no difference between my video response while using the computer before or after.  (This is just a test computer, not a mining rig, so the graphics card is doing double duty for the mining and regular computer usage right now.)

I'm just trying NSGminer on my desktop PC to see if I can get it to work.  The card is AMD R9 270, NSGminer 0.9.4, to GoByte pool.

I'm getting about 20 kh/s which seems really low, based on a few benchmark sites I looked up.  Is this right or is something wrong?

I will eventually be mining on NVIDIA 1070s, but just doing proof of concept right now.....

edit: also I notice when hitting G during execution, my GPU temp is only 53, which seems very low.  So maybe the intensity is too low, but still this wouldn't seem to account for such a low rate, unless I'm misunderstanding something.