Yes, it is all very subjective. I have found the exact same thing with various people reporting on how well a Rostra works on a C-14 for example, some think it is wonderful while some seem a little disappointing that it is not flawless. Exactly as you said, how does one measure pain, food, etc., etc.
I will say that I have not found any 'day and night' differences in C-14's regardless of tune or flash (though of course I have not tried them all). But I did notice a huge difference in an '08 ZX 14 once the 'flies were removed AND it was tuned on a dyno with a Power Commander. An acquaintance had a new ZX and frankly both of us were underwhelmed with its performance in low to mid- range power, throttle response and so forth. I removed the 'flies and honestly, while it perhaps did get better, it was just not impressive, at least to either of us. But after adding a P.C. with a custom map, it was transformed into the bike I expected it to be in the first place- very impressive, far more so than tuning a C-14 for example.
I was happy with removing the 'flies and a P.C. III with a custom map on my own bike, coupled with removing all the slack from the throttle cables which I personally found to contribute more to the bike's low- speed jerkiness than the actual mixture tuning. But just like you, I would not say it was suddenly something outrageous, just more like the 1400 cc bike I expected when I bought it in the first place. I found the stock bike neutered below, say, 5K RPM, and removing the 'flies and re-tuning the mixture eliminated that situation.... IMO of course.
Brian
For me, it [Guhl flash] was a huge change and I was sure it was there. I wasn't expecting a "totally different bike" kind of experience, though. But it immediately got rid of that horrible lag and "sag" in the performance curve at lower RPM that was driving me crazy. I had the EXACT SAME issue with my ZRX-11- it felt the same way, until I installed a jet kit and WHAM, it was just linear after that. So if you know what it is was that was annoying, and had reasonable expectations, it was extremely noticeable and a "huge" change, at least with my driving style. If you have a different driving style or weren't bothered by the stock behavior to start with, it might be much less noticeable.
Well, subjectivity always comes across with wild variations. Kinda like explaining pain or how delicious something is. I know for sure that lots of things that annoy me or drive me crazy don't phase many other people at all, and vice-versa.