Upgrade worth it options? 9500amdphenom x4 asus m3a

Hello here is my system specs currrently not sure wether to simply go from my current amd pehnom x4 9500 to amd 9800 cpu and add another 4gb of corsair dominator ram upping my total to 8gb for about $200 usd total or should i simply scrap my current mobo and go with a new mobo cpu as upping the ram from 4gb to 8gb and uppingthe cpu wont be much of a difference?
main problem is i put in windows 7 and my pc seems to lag on some multitasking issues now and i never had that with windows xp.

any helps tips or suggestions would be greatly apreciated. would prefer the $200 budget option but if not feasible could do $300-$400 if it was a mobo cpu upgrade but would want one where i could end up adding in another radeon 5750 down the line i suppose thanks for looking!!

system setup is amd phenom x4 9500
4gb of corsair cominator ram cm2x2048-8500c5d
2tb hdd wd 64mb cache
1024mb ati radeon hd5750
asus m3a motherboard

cpu-id computer jargon details ram timings and such below..

Chipset
-------------------------------------------------------------------------

Northbridge AMD 770 rev. 00
Southbridge ATI SB600 rev. 00
Graphic Interface PCI-Express
PCI-E Link Width x16
PCI-E Max Link Width x16
Memory Type DDR2
Memory Size 4096 MBytes
Channels Dual, (Unganged)
Memory Frequency 400.0 MHz (1:2)
CAS# latency (CL) 5.0
RAS# to CAS# delay (tRCD) 5
RAS# Precharge (tRP) 5
Cycle Time (tRAS) 18
Bank Cycle Time (tRC) 23
Command Rate (CR) 2T
Uncore Frequency 1800.1 MHz

Memory SPD
-------------------------------------------------------------------------

DIMM # 1
SMBus address 0x50
Memory type DDR2
Module format Regular UDIMM
Manufacturer (ID) Corsair (7F7F9E0000000000)
Size 2048 MBytes
Max bandwidth PC2-6400 (400 MHz)
Part number CM2X2048-8500C5D
Number of banks 2
Data width 64 bits
Correction None
Nominal Voltage 1.80 Volts
EPP yes (1 profiles)
XMP no
JEDEC timings table CL-tRCD-tRP-tRAS-tRC @ frequency
JEDEC #1 4.0-4-4-13-16 @ 270 MHz
JEDEC #2 5.0-5-5-18-23 @ 400 MHz
EPP timings table CL-tRCD-tRP-tRAS-tRC-CR @ frequency (voltage)
EPP profile #1 (full) 5.0-5-5-15-22-2T @ 533 MHz (2.100 Volts)

DIMM # 2
SMBus address 0x51
Memory type DDR2
Module format Regular UDIMM
Manufacturer (ID) Corsair (7F7F9E0000000000)
Size 2048 MBytes
Max bandwidth PC2-6400 (400 MHz)
Part number CM2X2048-8500C5D
Number of banks 2
Data width 64 bits
Correction None
Nominal Voltage 1.80 Volts
EPP yes (1 profiles)
XMP no
JEDEC timings table CL-tRCD-tRP-tRAS-tRC @ frequency
JEDEC #1 4.0-4-4-13-16 @ 270 MHz
JEDEC #2 5.0-5-5-18-23 @ 400 MHz
EPP timings table CL-tRCD-tRP-tRAS-tRC-CR @ frequency (voltage)
EPP profile #1 (full) 5.0-5-5-15-22-2T @ 533 MHz (2.100