Please help -Sony FW 390, Dell Studio 15, or Asus N50?

Hi, I am trying to decide between these 3 choices, but I am having a hard time making the final decision – any help would be appreciated (hopefully before end fo the week when the deals below expire)! Here are the configs – all in Canadian prices:

Asus – 2 config's (only difference is processor – is 0.14 Ghz worth the $172?):

ASUS N50 Series N50Vn-X6 NoteBook Intel Core 2 Duo P8400(2.26GHz) 15.4" Wide XGA 4GB Memory 320GB HDD DVD Super Multi NVIDIA GeForce 9650M GT
@ $1,100

http://www.newegg.ca/Product/Product...82E16834220489

ASUS N50 Series N50Vn-X5A NoteBook Intel Core 2 Duo P8600(2.40GHz) 15.4" Wide XGA 4GB Memory 320GB HDD 7200rpm DVD Super Multi NVIDIA GeForce 9650M GT – Retail
@ $1,272

http://www.newegg.ca/Product/Product...82E16834220489

Dell Studio 15:

Processors Intel® Core™ 2 Duo P8700 (2.53GHz/1066Mhz FSB/3MB cache)
Memory 4GB Shared Dual Channel DDR2 at 800MHz
LCD Panel 15.6” Full High Definition (1080p) High Brightness LED Display with TrueLife™ and Camera
Video Card 512MB ATI Mobility Radeon HD 4570
Hard Drive Speed: 250GB SATA Hard Drive (7200RPM) with Free Fall Sensor

@$1,191 w/ 20% e-coupon expiring tm.

Sony FW390

Intel® Core™ 2 Duo Processor P8600 (2.40GHz)
ATI Mobility Radeon™ HD 3650 with 512MB vRAM
LCD 16.4" (XBRITE-FullHD™)
WLAN (802.11a/b/g/n) with integrated Bluetooth® technology
320 GB SATA Hard Disk Drive [7200 rpm]
DVD +/- R DL / DVD +/- RW / DVD-RAM Drive
Standard Battery
Titanium Gray
Microsoft® Windows Vista® Home Premium 64-bit (English only)
4 GB DDR2-SDRAM (DDR2-800, 2GBx2)

@ $1,337 w/ the $200 off e-coupon expiring May 30

Other issues:
- For the Sony, I could save $135 by having 2 gb of RAM and then changing it to 4gb of DDR3 RAM at another place for maybe $80? – is this a good idea or would this possibly void the warranty?
- Would the 1080p resolution on Dell's 15.6" screen make things too small and hard to read?
- Is there a large difference in mobility with a 16.4" (Sony)? I am not taking it on any planes, but would take it out locally (in car) – people keep telling me anything over 15"'s too much....

I think I might be moderately (possibly low) gaming, plus mainly work and entertainment/multimedia, and don't need blue-ray. The Asus carrying the video card is attractive at the low price though. However, the other 2 seems like great deals as well with much better screens and possibly better build?

Thanks a lot in advance for the help!!

MC