Dell Poweredge SC 440 as a desktop. Possibilities?

I have been given an unused and stripped-down Poweredge SC 440.  I am planning on turning it into a desktop for my parents, as I have a spare copy of Windows 10 and a 500MB SATA drive.  The system has the latest BIOS.

I have three queries.  These are regarding the maximum CPU possible, the maximum amount of RAM in terms of volume and speed possible, and the question of a graphics upgrade.

QUERY 1 =====

Currently it only has an Intel Pentium 4 630 (3.00GHz, 2MB L2 cache, 800 MHz FSB, LGA775, Prescott, SL7Z9).  I have read other forum posts about CPU compatibility, and it is very clear that the dual-core Xeon 3040, 3050, 3060 and 3070 suit this system.  However, I have also read reports of the quad-core Intel Core2 Quad Q6600 working in this system, but some people lay claim that they do not get the full 8MB of L2 cache with this.  Also, the quad-core CPU appears to use 105W compared to the 65W of the Xeon CPUs.  Also, I have read about someone using a Xeon X3220 as well.  The stats are listed below.

Intel Xeon 3040, 1.86GHz, 2MB L2, 1066MHz FSB, PLGA775, 65W, 65nm

Intel Xeon 3050, 2.13GHz, 2MB L2, 1066MHz FSB, PLGA775, 65W, 65nm

Intel Xeon 3060, 2.40GHz, 4MB L2, 1066MHz FSB, PLGA775, 65W, 65nm

Intel Xeon 3070, 2.66GHz, 4MB L2, 1066MHz FSB, PLGA775, 65W, 65nm

Intel Xeon X3220, 2.40GHz, 8MB L2, 1066MHz FSB, LGA775, 105W, 65nm

Intel Core2 Quad Q6600, 2.40GHz, 8MB L2, 1066MHz FSB, LGA775, 105W, 65nm

So, does anyone have any real experience of using a Q6600 in this system, or shall I just go for a Xeon 3070 which I can pick up on eBay for £10?

QUERY 2 =====

RAM.  It is widely stated that 4x 1GB ECC unbuffered RAM is compatible, but there are suggestions that 4x 2GB is possible.  Some forum posts suggest that Dell limited this to 4x 1GB with one of the later BIOS updates, even though the chipset is said to accommodate 8GB in total.  Some clarity would be good on this.  Otherwise I will just run 64-bit Windows 10 with 4x 1GB recommended RAM.