It seems I can't go back to 2048x1536 display mode, I could with the closed source driver and I used to have fglrx working nicely at this resolution in the previous (Feisty) release with Beryl.  With the closed source driver I was having problems with the HSync blanking out whenever the screensaver kicked in.  Attached below is my original (working feisty) xorg.conf  Thus far, it seems everything has gone backwards for me, at least graphics wise.

# /etc/X11/xorg.conf (xorg X Window System server configuration file)
#
# This file was generated by dexconf, the Debian X Configuration tool, using
# values from the debconf database.
#
# Edit this file with caution, and see the /etc/X11/xorg.conf manual page.
# (Type "man /etc/X11/xorg.conf" at the shell prompt.)
#
# This file is automatically updated on xserver-xorg package upgrades *only*
# if it has not been modified since the last upgrade of the xserver-xorg
# package.
#
# If you have edited this file but would like it to be automatically updated
# again, run the following command:
#   sudo dpkg-reconfigure -phigh xserver-xorg

Section "ServerLayout"
	Identifier	"Default Layout"
  screen 0 "aticonfig-Screen[0]" 0 0
	Inputdevice	"Generic Keyboard"
	Inputdevice	"Configured Mouse"
	Inputdevice	"stylus"	"SendCoreEvents"
	Inputdevice	"cursor"	"SendCoreEvents"
	Inputdevice	"eraser"	"SendCoreEvents"
	Option		"AIGX"	"true"
EndSection

Section "Files"
	
	# path to defoma fonts
	Fontpath	"/usr/share/X11/fonts/misc"
	Fontpath	"/usr/share/X11/fonts/cyrillic"
	Fontpath	"/usr/share/X11/fonts/100dpi/:unscaled"
	Fontpath	"/usr/share/X11/fonts/75dpi/:unscaled"
	Fontpath	"/usr/share/X11/fonts/Type1"
	Fontpath	"/usr/share/X11/fonts/100dpi"
	Fontpath	"/usr/share/X11/fonts/75dpi"
	Fontpath	"/usr/share/fonts/X11/misc"
	Fontpath	"/var/lib/defoma/x-ttcidfont-conf.d/dirs/TrueType"
EndSection

Section "Module"
	Load		"i2c"
	Load		"bitmap"
	Load		"ddc"
	Load		"dri"
	Load		"dbe"
	Load		"extmod"
	Load		"freetype"
	Load		"glx"
	Load		"int10"
	Load		"type1"
	Load		"vbe"
EndSection

Section "InputDevice"
	Identifier	"Generic Keyboard"
	Driver		"kbd"
	Option		"CoreKeyboard"
	Option		"XkbRules"	"xorg"
	Option		"XkbModel"	"pc101"
	Option		"XkbLayout"	"us"
EndSection

Section "InputDevice"
	Identifier	"Configured Mouse"
	Driver		"mouse"
	Option		"CorePointer"
	Option		"Device"	"/dev/input/mice"
	Option		"Protocol"	"ExplorerPS/2"
	Option		"ZAxisMapping"	"4 5"
	Option		"Emulate3Buttons"	"true"
EndSection

Section "InputDevice"
	
	# /dev/input/event
	# for USB
	Identifier	"stylus"
	Driver		"wacom"
	Option		"Device"	"/dev/wacom"# Change to 
	Option		"Type"	"stylus"
	Option		"ForceDevice"	"ISDV4"# Tablet PC ONLY
EndSection

Section "InputDevice"
	
	# /dev/input/event
	# for USB
	Identifier	"eraser"
	Driver		"wacom"
	Option		"Device"	"/dev/wacom"# Change to 
	Option		"Type"	"eraser"
	Option		"ForceDevice"	"ISDV4"# Tablet PC ONLY
EndSection

Section "InputDevice"
	
	# /dev/input/event
	# for USB
	Identifier	"cursor"
	Driver		"wacom"
	Option		"Device"	"/dev/wacom"# Change to 
	Option		"Type"	"cursor"
	Option		"ForceDevice"	"ISDV4"# Tablet PC ONLY
EndSection

Section "Monitor"
	Identifier	"aticonfig-Monitor[0]"
	Horizsync	28.0	-	121.0
	Vertrefresh	43.0	-	66.0
	Option		"VendorName"	"ATI Proprietary Driver"
	Option		"ModelName"	"Generic Autodetecting Monitor"
	Option		"DPMS"	"true"
EndSection

Section "Device"
	
	# Manpage: Use  or  don't  use accelerated EXA DownloadFromScreen hook
	# when possible.
	# Wrongly defaults to 8MB sometimes, see your logfile.
	# Bigger seems better.
	# seemingly in XAA mode only
	# affected stability only positively on my system
	Identifier	"aticonfig-Device[0]"
	Driver		"fglrx"
	Option		"DRI"	"true"
	Option		"ColorTiling"	"on"
	Option		"EnablePageFlip"	"true"
	Option		"AccelMethod"	"XAA"
	Option		"XAANoOffscreenPixmaps"	"true"
	Option		"RenderAccel"	"true"
	Option		"AGPFastWrite"	"on"
	Option		"AccelDFS"	"1"
	Option		"AGPMode"	"1"
	Option		"GARTSize"	"64"
	Option		"VideoOverlay"	"on"
	Option		"OpenGLOverlay"	"off"
	#Option "AGPMode" "x" <- x may be 2 or 4 depending on your system
	# 1/0 On for PCIE, off for AGP
	# 1-8 Does not affect PCIE models.
	# 0-64 Megabytes of gart (system) memory used.
EndSection

Section "Screen"
	Identifier	"aticonfig-Screen[0]"
	Device		"aticonfig-Device[0]"
	Monitor		"aticonfig-Monitor[0]"
	Defaultdepth	24
	SubSection "Display"
		Viewport	0	0
		Depth	24
		Modes		"2048x1536"	"1600x1200"	"1280x1024"	"800x600"	"640x480"
	EndSubSection
EndSection

Section "DRI"
	Mode	0666
EndSection

Section "Extensions"
	Option		"Composite"	"Enable"
	Option		"Composite"	"0"
EndSection