Need advice on a GPU for XPS Studio 8000

I asked about this PC before and it has the hd radion 7750 made by asus, but it seems to be lacking quality with FFXIV ARR, it won't pull it on high and I think it even skips on mid-high settings, but we noticed the PC did have the 6 pin power connector for GPU's, is there a better GPU we can try? I asked back in June maybe a new compatible GPU came out, here's the PC Spec's, Thanks in advance.
the Dell Studio XPS 8000-2361JBK

Type Intel Core i7 i7-860 / 2.8 GHz
Number of Cores Quad-Core
64-bit Computing Yes
CPU Qty 1.0
Max CPU Qty 1.0
Chipset Type Intel P55 Express
Cache Memory
Installed Size L2 cache - 8.0 MB
Cache Per Processor 8 MB
RAM
Installed Size 8.0 GB / 16.0 GB (max)
Technology DDR3 SDRAM
Form Factor DIMM 240-pin
Features Dual channel memory architecture
Hard Drive
Capacity 1.0 x 1.0 TB
Interface Type Serial ATA-300
Spindle Speed 7200.0 rpm
Storage Controller
Type Serial ATA - Integrated
Controller Interface Type Serial ATA-300
RAID Level RAID 1,
RAID 0
Hard Drive (3rd)
Type None
Optical Storage
Type DVD±RW (±R DL)
Optical Storage (2nd)
Type None
Card Reader
Type 19 in 1 card reader
Supported Flash Memory Cards MultiMediaCardplus,
CompactFlash Card type I,
microSDHC,
Microdrive,
miniSD,
Memory Stick PRO Duo,
MultiMediaCardmobile,
Memory Stick,
RS-MMC,
MultiMediaCard,
SD Memory Card,
CompactFlash Card type II,
SmartMedia Card,
miniSDHC,
Memory Stick PRO,
MultiMediaCardmicro,
Memory Stick Duo,
microSD,
xD-Picture Card
Storage Removable
Type None
Graphics Controller
Type Plug-in card
Interface Type PCI Express 2.0 x16
Graphics Processor / Vendor NVIDIA GeForce GTS 240
Video Memory 1.0 GB
Input Device
Type Mouse,
Keyboard
Audio Output
Type Integrated
Sound Output Mode 7.1 channel surround
Audio Input
Type None
Telecom
Modem None
Networking
Type Integrated
Wireless LAN Supported Yes
Data Link Protocol IEEE 802.11g,
IEEE 802.11n (draft),
IEEE 802.11b,
Ethernet,
IEEE 802.11a,
Fast Ethernet,
Gigabit Ethernet
Compliant Standards IEEE 802.11b,
IEEE 802.11n (draft),
IEEE 802.11a,
IEEE 802.11g
Printer
Type None
Miscellaneous
Cables Included Power cable ( 1.0 pcs.)
Features Security lock slot (cable lock sold separately)
Expansion / Connectivity
Bays 2.0 (total) / 1.0 (free) x 5.25",
2.0 (total) / 1.0 (free) x 3.5",
1.0 (total) / 1.0 (free) x 3.5"
Slots 1.0 (total) / 1.0 (free) x PCI - LGA1366 Socket,
4.0 (total) / 0.0 (free) x PCI Express x16,
2.0 (total) / 0.0 (free) x Processor,
1.0 (total) / 1.0 (free) x PCI Express x1,
1.0 Memory
Interfaces 1.0 x Audio - Output ( 1 in front ),
1.0 x Audio - Line-in/microphone ( 2 front, 4 rear ),
1.0 x Audio - Line-out (side surround) ( 1 in front ),
1.0 x Audio - Input,
1.0 x Audio - Line-out (front surround),
1.0 x Hi-Speed USB - SPDIF output,
1.0 x Audio - Line-out (center/subwoofer),
1.0 x Network - Line-in,
1.0 x Storage - Ethernet 10Base-T/100Base-TX/1000Base-T,
1.0 x IEEE 1394 (FireWire) - Line-out (back surround),
8.0 x Microphone - eSATA,
1.0 x Audio,
1.0 x Headphones
Power
Device Type Power adapter
Power Provided 350.0 Watt

a Dell rep told my Girlfriend that the best GPU for her XPS is a ati radion hd 4850
the XPS has 8 gb ram and we removed the wifi adapter.