Can you try disable PPAA please?
If the crash is happening when playing custom MAP/MOD,try to reproduce the crash also in our official Arma III missions Escape from Stratis and Headhunters.

It was easy to reproduce those crashes in the conditions you mentionned : it happened after just a few minutes.
PPAA disabled, no mod, and occured on both Escape from Stratis and Headhunters.
RPT, bidmp, mdmp dxdiag and win7 crash reports in zip file : Arma 3 Alpha crashes 4991 v2

I still get a lot of those crash, can't play more than 5 minutes.
I tried almost everything : disabling DEP in win 7 and in BIOS, underclocking my GPU, put an old trackir software (tracktool), putting older version of AMD catalysts...
I still get this crash most of the time :

Nom d’événement de problème: APPCRASH

  Nom de l’application:	arma3.exe
  Version de l’application:	0.53.103.478
  Horodatage de l’application:	5150d486
  Nom du module par défaut:	arma3.exe
  Version du module par défaut:	0.53.103.478
  Horodateur du module par défaut:	5150d486
  Code de l’exception:	c0000005
  Décalage de l’exception:	005cc833
  Version du système:	6.1.7601.2.1.0.256.48
  Identificateur de paramètres régionaux:	1036
  Information supplémentaire n° 1:	0a9e
  Information supplémentaire n° 2:	0a9e372d3b4ad19135b953a78882e789
  Information supplémentaire n° 3:	0a9e
  Information supplémentaire n° 4:	0a9e372d3b4ad19135b953a78882e789

And RPT

Server: Unhandled user message Type_109

Server: Unhandled user message Type_109

Exception code: C0000005 ACCESS_VIOLATION at 00831996
Allocator: F:\STEAM\steamapps\common\Arma 3\dll\tbb4malloc_bi.dll
graphics: D3D11
resolution: 1280x1024x32

...

Distribution: 0
Version 0.53.103478
Fault time: 2013/03/26 19:05:46
Fault address: 00831996 01:00430996 F:\STEAM\steamapps\common\Arma 3\arma3.exe
file: COWholeLottaStratis (__cur_mp)
world: Stratis
Prev. code bytes: 05 0F 28 C2 EB 03 0F 28 C7 F3 0F 10 89 04 03 00
Fault code bytes: 00 0F 2F C8 76 05 B0 01 C2 08 00 F3 0F 10 1D 4C

Registers:
EAX:01C3C69C EBX:0A8B5D00
ECX:01C3D04C EDX:01C3C690
ESI:01C3D04C EDI:00000000
CS:EIP:0023:00831996
SS:ESP:002B:01C3C668 EBP:00000000
DS:002B ES:002B FS:0053 GS:002B

Flags:00010203

note: Minidump has been generated into the file C:\Users\Marc\AppData\Local\Arma 3 Alpha\arma3_2013-03-26_18-51-43.mdmp

crashdumps are from old version 0.51.103185.

Can you clean crashdumps folder and upload crashdumps from last version please?
actual version is:
Type: Public Alpha
Branch: Stable
Version: 0.52.103507

Thank you.

Last bunch of crash reports with latest dev build uploaded.
One crash occured in main menu after just 1 minute after launching the game.

Two more reports and minidumps when trying to switch between memory allocators dll contained in devbuild and win7 64 native ones.

Another one in SP (infantry showcase). Seems to be the same as the first one I reported.

Last devbuild + no PPAA + no mod
AMD7850 + 13.3 beta driver
Zonealarm firewall in game mode.
Trackir 3 pro + Trackir software 5.2
win7 64
i53750K @ 4.4 ghz (stable oc on every other games)

I still can't play more than 5-10 minutes...

Do note that it seems that I got ride of those crashes when uninstalling Zone Alarm AND downclocking my CPU to 4.3Ghz...
It is strange because when I keep Zone Alarm installed and I push down my CPU overclock to even stock clock, I still encounter those crashes.

At 4.4Ghz, my cpu is stable with multiple games (combat mission afghanistan, DCS black shark, mass effect3) and I can run an OCCT stress test during one hour without errors.

It seems that it is the combination of Zone Alarm + a high CPU overclock that makes the game crash.

This is typicall Zone Alarm issue. Lot of players had this problem, until they did uninstall Zone Alarm.

I have this issue of random crashes and i do not have Zone Alarm

To Sgt.Sai:
Create own report with crashdumps please and we will look at them. Thank you.