has it been decided yet if the .43 cal rap4 can be used?
Yes we have decided you may use it 
What FPS are you going to allow them to shoot at?
OK to begin with I must say this has been a long time in coming and agree with alot of what others have said in that they can't wait ...
Just registered here and been reading thru as many posts as I can saturate my poor brain with LoL...
Now onto the real question at hand....
With most fields being regulated at under 300fps , the question which comes to my mind is that for a .43 paintball to be as powerful as a .68 ( meaning to hit with the same force/joules/energy/impact ) it would need to be travelling at 600fps , ie :
.40 and .43 cal paint is much lighter and hence less dangerous, the mathmatics behind this follows :
Power (joules) = [velocity (m/s) square * mass(kg)/2
so a .43 ball wieghs approx. .8grams so ....
.43 at 250fps : (76.20*76.20*.0008) /2 = 2.32 joules
.43 at 300fps : (91.44*91.44*.0008) /2 = 3.34 joules
.43 at 350fps : (106.68*106.68*.0008)/2 = 4.55 joules
.43 at 400fps : (121.92*121.92*.0008)/2 = 5.94 joules
.43 at 450fps : (137.16*137.16*.0008)/2 = 7.52 joules
A .68 ball wieghs approx. 3.2 Grams so ...
.68 at 300 fps : (91.44*91.44*.0032)/2 = 13.37 joules
Meaning that for a .43 ball should be allowed on fields at speeds I belive to be safe of 550fps
The reason I went into this so far is that I own several .43 guns now and have been eagerly anticipating the day when this tpye of game was a reality.
I did not write the above algorythm I simply have researched ALOT on this topic and began purchasing my markers even fearing they would not be allowed to operate at the fps that I think they should be allowed to, I have shown the math to several local fields and at least one is considering it, however , I think it will take much more then math to bring thier insurance companies into allowing them to allow us at higher FPS which for this type of game would be a real plus , having a more realistic combat scenerio such as REAL snipers , longer straighter shots ect.
My apologies for rambling . Have a great one all,
~Ivan~