Bottlenecking / How far can I upgrade?

[kensai13]

I have 2 systems I'm trying to upgrade. My intention is to get the most bang for my buck out of Battlefield 3 while keeping muss, fuss, and costs down.

System 1)

Asus Maximus Formula mobo

Core 2 Duo E8400 3.0GHZ. Stock cooler

4gb ddr2 1066

Radeon HD6870 Asus

Corsair TX750 PSU


System 2)

EVGA 750I SLI FTW mobo

Core 2 Duo E8400 stable OCd to 3.825GHZ

4gb ddr2 800

EVGA GTX 470 SC

PCP&C Silencer 750 Quad black PSU


The BF3 beta is running ok on system 2, but not as well as I'd like.

-I've considered purchasing a second Gtx 470 from ebay (approx $175). My concerns here are 1)If the PCP&C Silencer will run the OC'd E8400 and SLI 470s. 2) Will the OC'd 8400 bottleneck the SLI Gtx470s. 3) Ditto for the memory.
-I've also considered selling my 470 and putting that money with the $175 earmarked for the SLI card. With this I could buy a high end Gtx570. I know the PSU will run it fine but concerns 2 and 3 still apply.

I haven't had a chance to run BF3 beta on system 1 yet but assume it's similar to slightly inferior to system 2's performance.

-I've considered purchasing a 2nd HD6870 for crossfire. I'm pretty sure the PSU will run this system ok. (unless I'm wrong). My concern here is once again bottlenecking but exacerbated by the stock CPU.

If I could buy these 2 cards and get good performance from dropping them in my systems I'd be in for around $350 and happy. This is my tentative plan unless my concerns listed above bear fruit.

Any thoughts?

 

[9_breaker]

(system 2)
TDP of 225W for each GTX470 ....so two would be 450 watts

add in CPU at 100-130 Watts --- 580 watts
add in other stuff ie ,HD's,ram,dvdburner
so I would probably consider a bigger PSU like 850 watt or higher

system 1

6870 wont bottleneck at 1080p

 

[kensai13]

This site: http://extreme.outervision.com/PSUEngine suggests a 738 watt PSU if I drop the OC to 3.6ghz. It says my cpu is only 92 watts at that OC.

This is using stock GTX 470s in SLI. I have the EVGA SC, but I suppose I could always use afterburner to clock them back a smidge to stock.

Also I forgot to say my intended resolution for both systems is indeed 1080P.

 

[9_breaker]

i just thought of an average cpu consumption . you could get the 470 but first downclock the cpu . then use this

http://www.ebay.com/itm/Zalman-Multi-Fan-Controller-ZM-MFC2-/120761712403

to check if your power consumption is low enough to oc . i havent heard of any software that can check your power consumption so thats the best option.