One key difference between these boards is the expansion slot design, which IMO will affect real world use quite a bit. If you're considering these boards (or any 1366 mobo, for that matter), then because of the large investment, make sure you look very closely at the slot design and how you intend to use them.
The eVGA board is capable of tri-SLI with dual slot video cards, while the P6T Deluxe is not. Tri-SLI is the raison de etre of the eVGA mobo. However, once you tri-SLI, then you can't even run a sound card and must use on-board. All of the expansion slot space is taken up when that happens.
If you really want to have room to do tri-SLI, then the better mobo is actually the Asus P6T6 WS Revolution because it has 3 lanes at x16 (the eVGA doesn't--its last lane / bottom slot is at x8). For this reason, I think that it is slightly better than the eVGA. However, it will be a while before running 3 GTX 295s (or 4870x2s) has been fully optimized but hey, it doesn't hurt to plan farther into the future when spending this kind of cash.
Other boards can tri-SLI too, but the third card will hang off the end of the mobo and also cover up some of the bottom edge connectors (e.g. Asus Rampage II Extreme and Gigabyte EX58-UD5).
IMO, the Asus P6T Deluxe is better oriented for real world use in this department. For example, you can run 2 dual slot video cards, with space in-between them for better cooling, and have room for a PCIe sound card as well. The extra space between the video cards is the legacy PCI slot, which can also be used for a RAID controller, wireless network card, etc. Expansion-wise, I think that this is a better setup for real world use.
If you're only going to use 2 video cards max, then I'd go with the P6T Deluxe for its overall expansion flexibility and superior video cooling design over the eVGA. Note that most X58 boards do not have space between the 2 video cards (e.g. Asus Rampage II Extreme and the Gigabyte boards). The eVGA also puts 2 dual slot cards next to each other without extra cooling space when running SLI.
Finally, if you're interested in the P6T Deluxe and are not in a rush, check out the Asus website as they have a P6T Deluxe V2 listed, but it's not yet generally available. This may hint at potential issues with the current "V1".