To overclock or upgrade

Hello all,
I'm having issues running a game that I believe I should be able to, and I am trying to determine the extent to what I need to do to fix it, either to overclock components or upgrade some. The game is called Battlefield BC2 and the minimum requirements are Here

I'll attach more specific details below, but my rig falls in between the minimum and recommended and in summary looks like this:
• Processor: Intel Core 2 Duo 8500
• Main memory: 4GB
• Graphics card: Radeon 4870
• Graphics memory: 512MB
• OS: Windows Vista 32x
• Free HDD space: 60GB

When I play the game standalone, I can play with the high settings without issue. When I play online I've reduced my settings to Low and while this often allows me to play at an acceptable level, other times there is perceptible lag in action. Both my latency and bandwidth appear to be acceptable (bandwidth is 25MB down on Verizon FIOS).So I'm trying to narrow down whether I can OC the GPU, CPU, RAM to make this work better, or if I need to upgrade some of my gear (CPU / GPU). Here is what I have in detail, or what I have done to try to troubleshoot this. Any help is appreciated.

Additional Details:
LCD: Samsung 2232BW. Native resolution 1680x1050
BC2: Played at 1680x1050, LOW quality
GPUZ and CPUZ displays: Here

Troubleshooting:
- Downloaded latest drivers for the video card
- Modest overclock on the GPU using ATI Overdrive, seen here
- Tried to determine if GPU Memory was the bottleneck, however contrary to what I've read the latest version of GPU-Z doesn't have that in the sensor list, and I can' find another VRAM Usage tool for Vista (freeware)
- Tried to determine is CPU was the bottleneck, but can't find a way to actually create a log file from CPUZ while in game
- Have researched into overclocking CPU and RAM, but am a little nervous about trying it. Currently my rig has SpeedStep running that doesn't work well with a CPU overclock from what I understand, and playing in the BIOS is something I rarely do.
- At idle, on CPUZ I see my Core Voltage at 1.096, Core Speed at 2003.9, Multiplier at 6, Bus Speed at 334MHz, Rated FSB at 1335.9. When running BC2 I see my Core Voltage up to 1.208, Core Speed up to 3005.4, Multiplier up to 9, Bus Speed remains 334MHz, Rated FSB remains 1335.9.
- When ingame, my GPUZ shows GPU Core Clock at 825, GPU Memory Clock at 950, GPU Temperature averaging in the low 50's, GPU Load % in the 30-40 range with a few spikes into the 60-80 range, GPU Temp (Dispio) in the low 50's, GPU Temp (Memio) in the upper 60's, and GPU Temp (Shadercore) in the upper 50s
- My BIOS is currently is v2002, only one version more current at v2012 so I'm leery of updating that for potentially limited gain / potential risk