New office cabling: should we use CAT7 or CAT6a? [closed]

These connections are rated to carry these speeds at the distance specified:

         | 10/100Mb |    1Gb     |   10Gb     |   40Gb†    |   100Gb‡
Category |   100m   | 37m | 100m | 55m | 100m | 50m | 100m | 15m | 100m
---------+----------+-----+------+-----+------+-----+------+-----+-----        
  5      |     x    |  x  |      |     |      |     |      |     |     
  5e     |     X    |  X  |   X  |  X  |      |     |      |     |     
  6      |     x    |  x  |   x  |  x  |      |     |      |     |     
  6a     |     X    |  X  |   X  |  X  |  X   |     |      |     |     
  F/7†   |     x    |  x  |   x  |  x  |  x   |  x‡ |      |  x‡ |     
  Fa/7a† |     X    |  X  |   X  |  X  |  X   |  X† |   X‡ |  X† |   X‡ 

Legend:

• Unless otherwise noted: The specification has been formalized and accepted. Keep in mind that the end-to-end cabling needs to be rated according to the category or you can expect reduced distance (since it's a digital system it normally either works or doesn't, though you can limit the speed of the connection to possibly allow functionality).
• † These are draft specifications. No guarantees, but it's reasonably safe to assume the final specification will be substantially similar.
• ‡ There is some reasonable speculation that with advances in circuity these connections will be possible. However, with current technology they do not work.

Notes:

• Cat7 is officially known as CatF, and Cat7a as CatFa, in the current draft. This may change to be consistent with the previous numbering scheme, or they may keep the letter designation.
• 40GbE and faster does not use the RJ45 connection, it uses GG45. There is a connector known as ARJ45 which has pins for both, and is intended to be an intermediate step.
• I've seen cables advertized as Cat7/Cat7a without the GG45 or ARJ45 ends, these may be just Shielded lower grade cables since there is no "7" yet. There is no official specification to which manufacturers would have to adhere.

More information on the various Ethernet standards is available in my answer to What is the clock frequency inside 10Gb and 100Gb Ethernet cards?

I'll take a contrarian view here.

There is nearly no value in going from cat5e to cat6a in almost all office environments.

10gb copper is nasty, expensive, and flakey. It uses far more space than 5e, is heavier, and is harder to install. You have to fully test the entire cable plant including your patch cables if you want it to work. And by test I mean "use a cable tester" not "plug a computer in and watch a link light come up". And it gets you nothing unless you're going to actually run it at 10gb -- because 1gb works just fine on the cheaper stuff and doesn't work better on the expensive stuff.

If you're going to be going 10gb/sec because you have legit reasons (you do geology / video / VM image work / etc) -- skip the copper. Go straight to fiber. But even that only gets you 10gb because the 40gb standard requires 4 pairs per link.

Another option is to only wire up those specific ports that actually need the 10gb over copper and just use 5e for everything else. Otherwise you'll be spending 10x as much money as you need to for those VOIP phone ports.

If this is a greenfield deployment just have them run conduits and leave cable pulls in place -- that way you can pull what you need right now and replace it with what you need later, rather than spending a huge amount of money installing FDDI and ATM everywhere.

No great choices...

Cat7 has different plugs, make sure you get ones with GG45 connectors, as they are backwards compatible to RJ45 (8P8C).