Improving real-time playback

Hello all,

Please forgive me if I ask an ignorant question or make stupid assumptions, (I'm new to HD editing)

I'm working on an animation project that I'm currently editing on Premiere Pro 2 at 1920x1080 24p with 8bit RGB Tiff sequences.

My machine:

Win XP Pro 32bit
Intel DX38BT board
Core 2 Quad QX9650 3Ghz
4GB DDR3 RAM
nVidia Quadro FX 1700
(It's really a 3d animation machine)

I used to render every edited sequence into a compressed AVI to get decent playback of the edit and the transitions,
But since the project is getting bigger and bigger,
I decided it was time to get better storage that will have enough capacity for the whole movie, be safe, and be fast enough for real-time playback without needing to render every edit to compressed AVI.

So I did some reading, and got a Rack mount Infortrend Eonstor with a 12 SATA drive Array connected through PCI-e x8 SAS, configured as RAID 5+hotspare.

The reason I bought such storage without adding or assembling a workstation with an editing card, is that as an animator I never really needed to do much capturing,
And I thought I may get along with just premiere editing in desktop mode relying on the storage speed for performance.

Using the RAID there is a significant playback improvement,
Premiere now plays the sequences quite smoothly (if not real-time) apart from the occasional "burp" especially during transitions (mainly cross dissolves).

The thing is I think the storage is capable for much more than that.
I did tests using the AJA System test Utility,
For uncompressed HD and 2k formats and the results vary between around 450MBps to around 700MBps.

My Questions are:

Do editing cards like AJA XENA, or BMD Decklink improve video playback and transitions?
Or do they just provide IO connectivity and enhanced video file support?

What is the relation between CPU, GPU, Editing card, and storage, in providing good playback in Premiere Pro?

Do I need an Editing card, or Invest in a more powerful GPU?

Do I need to get a server board and two Xeons?
(right now premiere is using about 15 to 20 percent of the 4 cores in the machine)


Thanks in advance for any tip, or info on the subject,


Oded