David, you're from a hard science field where papers are more rigorous.
Unfortunately, when it comes to nutritional studies, most are not. You have to take the punchline with a grain of salt.
Case in point, your quoted study:
1. Sample size is 7.
2. "Normal men". Men who engage in serious weight training do not belong to this category.
3. Ten days.
1) Sample size of 7 is irrelevant if the effect is large. What matters is the product of effect and sample size, that's what determine statistical significance.
2) I had already posted about weight trainers previously.
3) 10 days is what's measured.
If you want to put your health at risk by consuming too much protein, do so. It's not going to build you more muscle if you're going above ~0.8 grams per day per pound of lean body weight, which for most people means that ~120 grams a day of protein is the maximum effective dose, and even then only for newbie bodybuilders. Once you already have a lot of muscle you will be building very little new muscle tissue, so you will need less protein.
If you want to build 20 lbs of muscle in one year, you'll need an extra 25 grams of protein per day assuming perfect inefficiency, therefore a little more due to inefficiency of digestion. The links I included earlier suggest an extra 50-75 grams of protein a day for beginner bodybuilders, not an extra 300 grams a day.
Finally, your points are also moot as the link between too much protein and a drop in testosterone has since been corroborated by other studies.
High-protein, low-GI diets cause a dip in the free androgen index
http://www.ncbi.nlm.nih.gov/pubmed/17448569
Higher protein, lower monounsaturated fat, lower saturated fat, linked to lower testosterone in men who exercise
http://jap.physiology.org/content/82/1/49
And so on, it's a well-known result and is consistently measured across different studies. Too much protein => low testosterone. It makes sense intuitively: your body is very slow at digesting protein and converting it to glucose. If you're taking 350 grams of protein a days spread in 10 meals over 16 hours, you basically have continuous, massive quantities of glucose entering your bloodstream.
For greater testosterone, I'd recommend replacing some of that extra protein with saturated animal fats. For example, eat a 100 gram lamb steak rather than a 100 gram chicken breast.