Replacing a malfunctioning ATI video card from Dell computer

I need help on a comparable or better video card. I inherited this Dell Machine, so please don’t hate.
My issue is a malfunctioning ATI 5970 video card. This is my second card from dell within a 1 year period that had the same issue, pixel blocks that keep appearing and reappearing no matter what I do (change monitors, replacing cords, plugging the card in and out, different resolutions, settings on high res or low res, reformatting the hard drive, running games in windowed mode, updating drivers, etc, etc)
I have a pretty nice monitor Dell U3011 and I believe the rest of my system is ok for gaming, but what should I be looking for in a card?

I only want to run 1 monitor and want the ability to have crystal clear 2560 x 1600 resolutions.
I’ve been thinking: GTX 690 ($1000), GTX Titan ($1000) or a Radeon 7990 ($600).

Using only 1 video card and 1 monitor, do I need the more expensive cards?
Will the less expensive card give me what I want (same or better quality than I currently have)?
Are the 3 cards mentioned a major or minor step up from my current ATI 5970?
I hear about ATI releasing new cards soon, should I wait? If I do wait, which should I be looking at (again keeping in mind I only want 1 video card with 1 monitor)?

Below are the pertinent portions of my DxDIag:
OS Windows 7 Home Premium 64-bit (6.1, Build 7601) Service Pack 1
System Manufacturer: Dell Inc. Studio XPS 9100
BIOS: ?AcpiOemRevision(4.5)(0)(),?AcpiCreatorRevision(6.7)(1)(),&, \
Processor: Intel(R) Core(TM) i7 CPU X 980 @ 3.33GHz (12 CPUs), ~3.3GHz
Memory: 24576MB RAM
Available OS Memory: 16384MB RAM
Page File: 2857MB used, 29909MB available
DirectX Version: DirectX 11
DX Setup Parameters: Not found
User DPI Setting: 120 DPI (125 percent)
DxDiag Version: 6.01.7601.17514 32bit Unicode

Card name: ATI Radeon HD 5900 Series
Manufacturer: Advanced Micro Devices, Inc.
Chip type: AMD Radeon Graphics Processor (0x689C)
DAC type: Internal DAC(400MHz)
Device Key: Enum\PCI\VEN_1002&DEV_689C&SUBSYS_25421002&REV_00
Display Memory: 4095 MB
Dedicated Memory: 1989 MB
Shared Memory: 2106 MB
Current Mode: 2560 x 1600 (32 bit) (60Hz)
Monitor Name: Generic PnP Monitor
Monitor Model: DELL U3011
Monitor Id: DEL4063
Native Mode: 2560 x 1600(p) (59.972Hz)
Output Type: DVI
Driver Name: aticfx64.dll,aticfx64.dll,aticfx64.dll,aticfx32,aticfx32,aticfx32,atiumd64.dll,atidxx64.dll,atidxx64.dll,atiumdag,atidxx32,atidxx32,atiumdva,atiumd6a.cap,atitmm64.dll
Driver File Version: 8.17.0010.1132 (English)
Driver Version: 8.980.0.0


Thanks ahead of time for any input you may have!