On number 1, I dont think either of them matter too much. .006 or .001 arrows fly the same for me and the magority of us on this forum. As or weight, I would tend to think that would have more effect. However, the difference in weight between arrows would have to be a minumum of 10 grains of greater between arrows to make any real difference at the distances we shoot.
Number 2, depends on the bow, Release of fingures. It also depends on if you really care about tuning. For example, shen I first started shooting archery I was getting groups of 1" at 30 and 40 yards with a GT 5575. When I got and shot my broadheads the where flying low and left, I didnt know anything about tuning at the time. After learning about tuning and trying to paper tune the arrows I found that I had to switch to a 340 or 300 spine arrow to get consistant flight with the broadheads. I could still shoot 1" groups the differance was the broadheads where following my field points much closer. So, no spine dont matter in compatition as much as in hunting.
"When a hunter is in a tree stand with high moral values and with the proper hunting ethics and richer for the experience, that hunter is 20 feet closer to God." -Fred Bear
2012 Martin Cougar FC, Fury XT cam
CE PileDriver arrow, 535 grains