Graphic Card Strategy for non-gamer

I recently purchased a refurbished HP 6005 Pro MT Tower.  It is a bare bones machine that is running on Windows 7 Pro Service Pack 1 (64 bit) When I first turned it on, the on board graphics card did not support WebGL content.  I had previous problems with blacklisted video cards and drivers so I went to Ebay and bought an ATI Radeon HD 4650 1GB PCI-e 16 pin Graphics Card.  I installed this card and Downloaded the Catalyst Software that supposedly contains the correct drivers. What I didn't understand was that I would need to get a VGA to DVI-I adapter to plug the monitor directly into this card.  I found this out when the Display would not initialize after a reboot with the new card inserted.

I removed the new card and noticed that the Catalyst program was working, and that my installed Graphics Card was showing as ATI Radeon HD 4200.  I checked the internet and saw that I am now able to see WebGL content.  Went to DxDiag and saw that the onboard Graphics Card was indeed listed as ATI Radeon HD 4200 with 3166 MB of memory.

I then went to HP to find specs for Graphics in the HP 6005 Pro MT Tower and it was listed as a "Multi-head solution" with the following cards listed:

Radeon HD 4550 256 MB; Radeon HD 4650 1GB PCIe x 16; NVIDIA Quadro 290; and NVIDIA Quadro 290 PCI-x16.

My question is this:  It seems like the on board Radeon HD 4200 3GB is a better card than the HD 4650 1GB that I bought.  Are there any advantages to buying the VGA to DVI-I adapter that I would need to use the new HD 4650 card, and installing it as a 2nd GPU?  Asked in a different way, what could I use the 2nd GPU card (Radeon 4650 1GB for?

Any advice would be appreciated - Reggie