HeavyHemi

Cool GTX
Alan
Nice rig.
Give this a look:  http://www.accellcables.com/collections/adapters/products/ultraav-displayport-1-1-to-hdmi-1-4-active-adapter?variant=729675009
 
P/N: B086B-003B-2 - Poly Bag  $32.99 USD
Use the where to buy tab, several choices.
 
excerpt:

UltraAV DisplayPort 1.1 to HDMI 1.4 Active Adapter

The DisplayPort to HDMI adapter works with both DPCP (DisplayPort Content Protection) and HDCP (High- Definition Content Protection) ensuring full compatibility and successful transmission of all audio and video content. The adapter also supports uncompressed 8-channel audio and extended color depths delivering the flexibility to meet most computer application needs. This Type 2 dual-mode active adapter supports computer resolutions of up to 1080p@120Hz, 4K Ultra HD, stereoscopic 3D and requires no external power*.
*Please note, all features are subject to the capabilities of the computer and graphics solution.

AMD Eyefinity Multi-Display Validated

The Accell UltraAV DisplayPort to HDMI Active adapter is AMD Eyefinity certified, providing optimal experience when using AMD Eyefinity Technology and allowing 3 monitor configuration. This validation is awarded only to those products that have undergone extensive synthetic and real-world testing.
• Supports up to 4K Ultra HD and 1080p @ 120Hz
• Up to a 300 MHz clock rate for stereoscopic 3D support
• Compliant to HDMI 1.4b and DisplayPort Dual-Mode v1.1
• Plug and play, no software to install or external power needed
• Available in Mini DisplayPort version

• Compliant with DisplayPort 1.1 specification and HDCP 1.3
• Compatible with DisplayPort 1.2 High Bit Rate (HBR).
• Compliant with HDMI 1.4b specification, up to 300 MHz for 3D displays
• Maximum Resolution: 4K Ultra HD and 1080p @120Hz
• Plug-and-play on Windows systems
 
Warranty: 2-Year Replacement

It does not state it supports 4K @ 60hz.

stickywulf
Displayport and HDMI have some similarities but aren't technically compatible. Even the most basic DP>HDMI cable has an adaptor embedded within it to convert the signal. Even though the OP describes looking for a displayport to HDMI cable, in reality you're just trying to find an appropriate adaptor (regardless if it's embedded in the cable or a separate entity).
 
The choice of adaptor is understandably confusing considering you need to choose between passive, active and also the different DP and HDMI standards.
Essentially, all that you are looking for is something which will transport TMDS data on a 600MHz clock rate. This will provide the bandwidth you need for 4K @60Hz over HDMI.
 
As Cool GTX Can attest, you will have great difficulty locating one of these adaptors on the market today.
If you look at every cable or adaptor linked to in this thread you can see they are all 300MHz - which is only capable of 4K @ 30Hz.
The 6' cable you are looking at on Newegg was obviously a typographical error since the page now has no mention of displayport.
 
On the bright side, in September last year VESA announced Displayport version 1.3, which includes dual mode for TMDS data capable of 600MHz.
You can be assured that the cables are coming, just keep an eye out for DP > HDMI cables in the near future advertised as either DP1.3 or with a 600MHz clock or with HDMI 2.0. One of these has been spotted at CES 2015 a few weeks ago so it shouldn't be too long until they are available to buy.