My understanding is that the primary thing that l-arginine does is dilate blood vessels, and can cause a modest drop in blood pressure. I’ve stacked 2400mg or 4800mg of l-arginine with Viagra and yohimbe, and the combination (for me) works better than Viagra alone. But that combo does make my heart race a little as it compensates for the lower blood pressure. I wouldn’t recommend it if you’re on any sort of heart or blood pressure medicine.
There’s quite a bit about l-arginine on the web; a simple search will reveal a lot. In one place, I read that it takes about 4000mg for a therapeutic dose. As for sources, I looked on Amazon and Ebay, and found a few reputable sellers with a good price.
The only possible benefit I could see with PE is improved circulation might help when using a hanger or extender.