Upgrade XPS 8100 GPU for video editing? (from GTS 240 --> GT 630 Kepler)

I have older XPS 8100 with 350 W power supply, PCIe v2.

It comes with Nvidia GTS 240

• 112 CUDA cores
• 1 GB DDR3 128-bit memory

Is it good idea to upgrade it to GT 630 Kepler that has more CUDA cores and bigger memory BUT less bandwidth! Note there are several flavors of the GT 630 card. The Kepler one has more CUDA but lower memory bandwidth. It also uses a 28(?) nm architecture so it uses less power...

• 384 CUDA cores
• 2 GB DDR3 64-bit memory 

I am just trying to give my older desktop a bit of a boost so I can keep it a while longer. Just getting into video editing (simple talking heads HD videos from Canon DSLR mainly for web/YouTube but may experiment a bit with After Effect too)

The other upgrades I am planning:

• Replace main (and only drive) with a SSD drive for OS
• Add SATA III /eSATA controller card (motherboard currently supports only SATA II)
• Add 1 or 2 7200 RPM drives (WD Black Caviar or Seagate Barracuda SATA III) though thinking instead of having them in RAID 0 for increase speed I would just have them separate so I can use different drives for data, sources files on one, and previews, cache, etc. on the other
• Add USB 3 so I can also external docks if need be, like maybe keep my second drive internal and the third drive external but connected via eSATA III or USB 3

Given the hassle and expense, I am not planning to upgrade the i5 processor (1st generation I think) or the power supply. Is the system otherwise "balanced" for what I will be using it for?