I have been hitting Srixon for about three years now. I started with the SoftFeel and graduated to the Z Star whites as I started getting my game back after knee surgery. Last year I decided to try the Z Star yellows, and I love them. Besides being easier to see, I noticed that they are better around the greens.
Recently I also took some lessons to get my driver more on track. I had a bad over the top dead pull after the knee surgery, for about two years. After a lesson and buying Bobby Wilson's Long Drive Series, I am hitting a driver longer than ever before. I tested with both the white and yellow Z Stars, and to me there was a noticable difference. It may all be psychological, but I don't think so. It may be that they are just easier to see by us old guys....and kind of has a calming effect because of the color.
Anyway, I went from 21 handicap to 13 with game inprovement (yes better clubs), but also because I went to what I believe is a better ball. Also, if you are looking to buy a dozen, get them on eBay instead of some retail or online store. They are not close to $45. I get them for about $27 or $28 a dozen, but then I usually also buy six dozen at a time.
Ken