I'm wihth Paintballer,
Here is exactly what I would do for a non-enterprise xw6600 build:
| EVGA GeForce GTX 1050 Ti SC GAMING
|
The "SC" makes a big difference, in my experience. I like EVGA. Is 150.00 USD too much? And, I max out the xw6600 to the highest performance processors HP certified for them, two total. Those are the E5450 Xeon processors, sSpec code SLBBM to look for on eBay (about $15.00 USD each with shipping included). Plus, single 320 series 300GB SSD system/applications drive, with a big 2TB or smaller SATA II documents HDD (or SATA III HDD if it is HP branded). W7Pro64 or W10Pro64 properly installed, clean.
6 x 2GB or 6 x 4GB HP memory. Don't need 6 x 8GB, personally. Make sure to fill all 6 slots with identical RAM whatever you choose. This is for best speed, and is important.
That card can run at best speed in a PCIe Generation III slot, but is backwards compatible to slower generation slots. Your xw6600 has two PCIe Generaton II slots.... the two video PCIe 2 x16 slots. The others are Gen I. Put that card in the top PCIe 2 x16 slot. I'd say most, not "many", users cannot tell the difference between a PCIe Gen II vs a Gen III card. Maybe "almost all". You get the point..... Gen II versus Gen III is not the weak link.
Video cards themselves have been the weak link.... now any more. Invest in that plus SSD for best bang for your buck. Rocket ship with HP quality, for budget conscious users.