Help me decide which fans to get

Case: NZXT H2

Current fans:
Stock 120 mm NZXT fans x2 at front
Stock 120 mm NZXT fans at back
Stock fans with Noctua NH-D14

I have one empty slot for a 120 (140) mm fan and one for a 140 mm fan.
I am also considering to add a third fan to my NH-D14 as well as changing the cooler (reference) for my XFX 6970.

Questions:

1) Which 140 mm fan should I get? I've been looking at Noctua's NF-P14, any other suggestions?
2) Apparently the NF-P14 fits in the bottom 120 mm slot, so I guess I'll use the same fan there as the answer for 1) (unless a 120 mm does a better cooling job?).
3) According to others with the H2, they've gotten better temps and sound levels when they've traded their front stock fans to other fans. Question here: what's better, Noctua's NF-P12 or Scythe's Gentle Typhoon? I know the GTs are good with heatsinks, but what about sucking air into a case?
4) Like I said, I have the stock fans with the NH-D14, do you think I will have any benefit from changing the NF-P12 there to, say, a GT?
5) I read a thread about adding a third fan to a NH-D14, http://forums.extremeoverclocking.com/showthread.php?t=..., do you think it's worth it?
6) What do you guys think about changing my reference cooler on my 6970 to an Accelero XTREME Plus II? Can you recommend a better cooler?

I know it's hard to say that one fan is better than another, but considering I'll add five of the fans to a fan controller, I'll go for the one with superior cooling.

Thanks in advance!