I'm sorry if either of these have been discussed before.
1) It seems to me that if you don't know the answer to a problem but are able to eliminate at least one of the 5 choices, then it would be better to guess instead of leaving it blank. That's because with each problem wrong you lose 1/4 a point and each problem right, you gain a point. Thus, on average, you would gain and lose one point every 5 problems if you just randomly guessed. So, if you can eliminate even one choice, the odds would be in your favor to guess. Does this sound correct?
No you cant say anything about the state your going to be in 5 questions later. If youre guessing with 4 choices and a quarter point off all you can say is that it is very likely youre not going to gain any advantage. It is not a guarantee and its still possible to get screwed over by guessing even if you have only 3 choices.
for your 2) no not really, there are a few statistics in gradschoolshopper although programs really should have to report average PGRE.