Optiplex 780 Mini Tower Upgrade

Forgot to add that i would like to run 2 monitors for simple cad work 

Double wide cards will not go in.  So no its not ever an option.There is no point in upgrading a tower power supply due to this limitation.  A precision T3400 can take 2 full size cards with an upgraded power supply.  A corsair CS750M power supply would be recommended for the 580 as it has an 8 pin and a 6 pin power connection for 300W of video power.

Recommended 2 monitor card for CAD would be Quadro k2000

http://www.newegg.com/Product/Product.aspx?Item=N82E16814133484

Bare Minimum for 2 monitor cad would be K620

 http://www.newegg.com/Product/Product.aspx?Item=N82E16814133560

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Regulatory Model (Mini-Tower): DCSM or DCSM1F 

Regulatory Model (Desktop): DCNE or DCNE1F 

Regulatory Model (Small Form Factor): DCCY or DCCY1F

Regulatory Model (Ultra Small Form Factor): DCTR or DCTR1F

http://www.newegg.com/Product/Product.aspx?Item=N82E16814121439

 The slot is VERY Narrow.

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Optiplexes can only use 1 slot wide cards and have small power supplies.  The T3400 MAXES out at 16 gigs of ram and has a 525w POWER supply.

Precision T3400 525w (16gig) vs Optiplex 755 Tower 305w (8gig)

The T3400 Can Take 2 Radeon 5770's in Crossfire configuration and the 755 tower is limited a single Card like the Geforce 8800gs.

R7 250 OR Geforce 740 is the max for a 755.

My T3400 works fine with GTX 960 and does not require a power supply upgrade.

EVGA 02G-P4-2966-KR  GTX 960 2GB 128-Bit GDDR5 SuperSC ACX 2.0+ Video Card

http://www.newegg.com/Product/Product.aspx?Item=N82E16814487091

http://www.tomshardware.com/forum/356751-33-radeon-6450-250w says its ok but other sites say no

Thanks for the descriptive response

i think i'll grab the cheap one for now....

ASUS Radeon HD 6450

and see how that works 

i have an ati hd 3400 in there right now and its doing ok but not "great"

looks like i have a 255w psu will that card be ok?

also 8gb ram, 1TB Hard Drive 3.0 Ghz  if that matters

Thanks again