New AMD photoshop/gaming build with dual monitors

I am ready to order a new system this weekend. This will be my first complete build but I have replaced PCU, GPU and added memory, HD, CD drives to my old Athlon 3800 system from ABS (which still works fine, but is very slow).
I do have a couple of key questions. For photoshop applications is there a big difference between 4 and 8 GB of RAM and also how will 8 GB of slower RAM compare to 4 GB of faster RAM. Also, do you have any monitor recommendations. I currently have a Samsung 22in at 1680 x 1050. It is a great monitor but it will stay with my old system which my wife will keep. I will initially probably buy a 24in but plan to add a second monitor in the future which could be 1920 x 1080 or 1680 x 1050. Will the 4870 1 GB be sufficient for dual monitors or do I need a 4890?
Any recommendations would be appreciated

APPROXIMATE PURCHASE DATE: this weekend) BUDGET RANGE: US$1000-1200 (with 1 monitor)
SYSTEM USAGE FROM MOST TO LEAST IMPORTANT: photoshop, multitasking, gaming
PARTS NOT REQUIRED: I need everything except a keyboard
PREFERRED WEBSITE(S) FOR PARTS: Newegg but open to other sites
PARTS PREFERENCES: AMD but am open to Intel
OVERCLOCKING: Not at first but would like to after it is running smoothly CROSSFIRE: In the future but not now
MONITOR RESOLUTION: 1920x1080 I would actually like to have a dual monitor set up with 24 and 22 in monitors up to 1920 x 1080
ADDITIONAL COMMENTS: I am partial to the Coolermaster Storm Scout case.

Intial build from NE
Qty. Product Description Savings Total Price
1
XIGMATEK Dark Knight-S1283V 120mm Long Life Bearing CPU Cooler
Item #:N82E16835233029
Return Policy: Standard Return Policy $44.98
1
Nippon Labs 6 ft. USB2.0 A TO B CABLE
Item #:N82E16812816052
Return Policy: Standard Return Policy $4.89
1
GIGABYTE GA-MA790X-UD4P ATX AMD Motherboard
Item #:N82E16813128387
Return Policy: Standard Return Policy $109.99
1
Western Digital Caviar Black 640GB 3.5" SATA 3.0Gb/s Internal Hard Drive
Item #:N82E16822136319
Return Policy: Standard Return Policy $74.99
1
Sony Optiarc DVD/CD Rewritable Drive Black SATA Model AD-7240S-0B
Item #:N82E16827118030
Return Policy: Limited Replacement Only Return Policy $29.99
1
SABRENT CRW-UINB 68-in-1 USB 2.0 Internal Card Reader w/ USB 2.0 Port supports SDHC/VISTA
Item #:N82E16820300608
Return Policy: Standard Return Policy $12.99
1
SAMSUNG DVD Burner Black SATA Model SH-S223L LightScribe Support
Item #:N82E16827151188
Return Policy: Standard Return Policy $31.99
1
CORSAIR CMPSU-750TX 750W Compatible with Core i7 Power Supply
Item #:N82E16817139006
Return Policy: Standard Return Policy -$60.00 Instant
$20.00 Mail-in Rebate Card
$179.99
$119.99
1
Microsoft Windows Vista Home Premium SP1 64-bit for System Builders w/ Tech Guarantee
Item #:N82E16832116677
Return Policy: Software Return Policy $109.99
1
COOLER MASTER Storm Scout SGC-2000-KKN1-GP Black Computer Case With Side Panel Window
Item #:N82E16811119196
Return Policy: Standard Return Policy $99.99
1
Arctic Silver 5 Thermal Compound
Item #:N82E16835100007
Return Policy: Consumable Item Standard Return Policy $6.99
1
G.SKILL 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Dual Channel Kit Desktop Memory
Item #:N82E16820231189
Return Policy: Memory Standard Return Policy $79.99
1
Arctic Silver ACN-60ML (2-PC-SET) Thermal material Remover & Surface Purifier
Item #:N82E16835100010
Return Policy: Consumable Item Standard Return Policy $5.99
1
AMD Phenom II X4 955 Black Edition 3.2GHz Socket AM3 125W Quad-Core Processor
Item #: N82E16819103674
Return Policy: CPU Replacement Only Return Policy

HIS Radeon HD 4870 H487FN1GP Video Card
Item #: N82E16814161269
Return Policy: VGA Standard Return Policy -$6.00 Instant
-$20.00 Combo $350.98
$324.98
1
CPU Mag Gift - 6 free issues of CPU Magazine
Item #:N82E16800995076
Return Policy: Standard Return Policy $35.94
1
HIS Gift - Stormrise Game Coupon Bundle
Item #:N82E16800999372
Return Policy: Standard Return Policy $29.99
Grand Total: $1,052.85