Linuxboy,
thanks for the info. Several questions:
1. Is the PF just a product of the milk quality or some aspect of the process. My milk comes from mostly a jersey with very high cream (6% or better) but i think my solids are down this year overall due to their feeding habits etc. (This is a subjective feeling I have from the fact that my milk seems to be making less curds form the same milk amount.) I really can't know my pf without some kind of commercial testing process, right?
Yep, protein to fat ratio varies with the lactation cycle and feed. It's determined about half/half by genetics and feeding. In the summer time, during grazing, cows typically will eat less grain and less alfalfa. Also, when it's hot, all animals eat less in general. End result in the summer is lower fat, and slightly lower protein, which is great for most hard cheeses. If you feed 16-18% protein feed, the protein levels should be better. Jersey milk is terrific for cheddar, especially in summer. Your fat percentage seems fantastic, but might be a tad too high if you use raw milk for cheddar. Milk fat should be somewhere around 4-5% for cheddar, unless the protein levels are very high, such as feeding a bunch of alfalfa/timothy hay.
You do need to get a milk test if you want to determine the PF level. I can tell you how to do it at home, but it requires some lab equipment to do right. Kinda pricey.
If you're getting fewer curds from the same milk amount, it means your total non-fat solids, and possibly fat are lower. Basically, like you said, different feed, different yield.
2. How does cheddaring too long affect the cheese as far as texture and taste?
Have you ever had a cheddar where you bite into it, and instead of having a smooth bite completely, it's a bit crumbly, or when you break it off, it breaks off like the curds didn't mat well? Or a cheddar where it's a bit too sour and instead of tasting a cheddar bite, it doesn't have a balanced kick? That can be caused by cheddaring too much. Basically, too long of cheddaring means there's too much acid. This makes the curds not mat as well when you press, makes the final texture not as smooth, makes the paste/feeling not as plastic and combined.
3. Occasionally I have a cheese consistency that is very grainy right out of the press. By grainy, I mean that it mushes a little. It's like the exact opposite of the squeaky rubbery feel. It actually melts great and has been one of the family's favorite to cook with. Any idea what might have happened there?
Is it grainy when you mill and salt? Or does it become grainy after press? If the former, means you cheddared too long or used too much started and did not drain the whey fast enough. If it becomes grainy after press, but the curds were squeaky when you milled, means you didn't use enough salt, or the temps were too high when pressing, or the pH was too low when you milled, or you waited too long between milling and salting/pressing. Basically, means pH is a bit too low, likely around 4.9. It will still stretch, but be a bit more grainy. Your final cheese should not be bad, but likely will be more crumbly.
4. When milling the curd slabs which in my case are 5x5 inches and about 3/8 inch thick by the time I mill them (they started out 1 inch before stacking) what size curd cubes am I shooting for. 1/2 inch? 3/4 inch? 1 inch? bigger?
Well, you want the salt to penetrate evenly. That requires as close to a cube shape as possible for evenness, or the salt won't penetrate evenly on all sides. If your thickness is 3/8", then it should be 3/'8" strips or cubes. 3/8" is a good general size. 1" milled pieces are just too big for the salt to penetrate evenly and quickly.
Sorry to bombard you. Not everyday I get to talk to a real expert. 
Sailor, My daughter is looking for the camera. I'll try to post it tonite. It is a combination of electric fence wire, part of a wire freezer basket, and sunburn on the back of my neck. 
You're too kind, but I'm more of a science geek who likes getting the right answer than an expert. Happy to share my experiences, though
