I am admittedly far too lazy to read through a ton of answers but here is my opinion (feel free to blow through it)...
Progesterone levels and estrogen levels drop when you have a period. For that reason, most women will notice that their performance is BETTER when they are on their period because estrogen levels are lower and androgen levels are actually felt to be higher.
In the premenstrual phase, the progesterone and estrogen are at their highest levels and contribute to the bloat, moodiness, lethargy and dead legs feeling.
I have noticed that ALL of my PR's are the week of or right after a cycle would be (I had an endometrial ablation after my third child so I don't have the bleeding but I still ovulate, etc).
Short story is that your period (aside from being a mess if you are heavy bleeding) is actually a good thing from the anecdotal info.
Link here with lots of information....I think an earlier poster referenced part of it.
http://www.thinkmuscle.com/articles/volk/planet-estrogen-03.htm