Typically the features that you don't hear about from marketing are the ones that don't bring in all the money (e.g. pushed as "enterprise feaures" in order to sell Enterprise Edition). I answered a similar question here that provided a list of my favorite new features in 2012, that also aren't limited to Enterprise Edition:
What are Objective Business Reasons to Prefer SQL Server 2012 over 2008 R2?
(I could list them here but I don't think duplication makes sense. And there are some other good answers on that page as well.)
The only difference would be you could add to the list the things that have been added from 2008 on: date/time data types, data compression (Enterprise), backup compression (Standard+), some syntax improvements (multi-row values, inline declare + assign, +=/-=, etc). These are things you would get, though, whether you went 2005 -> 2008 R2 or 2005 -> 2012. Guess I knee-jerked listing those because you won't get them if you stay where you are.
In addition, moving to 2012 now instead of 2008 R2 buys you a longer lease toward end-of-life / end-of-mainstream support. However if you are using CAL licensing you might consider 2008 R2, because this option isn't available anymore in 2012 Enterprise. And core licensing can be more expensive if your CPUs have more than 4 cores per socket. They recently updated the "How to Buy" part of the site; you should stay on top of that and keep in good touch with a licensing rep. They're not perfect (and we can have a different discussion about this) but they're the only ones who can give you plausible deniability should anything they sell you end up putting you out of compliance, as long as you haven't lied to them. :-)
If you're going to take advantage of CPU-intensive things like compression, then having faster, fewer cores may be tolerable overall especially since it will make your SQL licensing (quite likely the most expensive part of your solution) that much cheaper. More, slower cores will be more expensive in terms of licensing, and spreading the work over more cores won't necessarily do any better for an OLTP-type workload - since many tasks cannot be parallel anyway. Also, AMD cores are subject to a core factor, which means the pricing is adjusted. This means you pay less per AMD core than per Intel core, but this is probably reflected in the performance, as well (at least if my conversations with Glenn Berry are any indication). No discount like this is in effect for 2008 R2 (at least AFAIK) since you're paying by the socket. Personally, I would rather spend the money on the better cores, but at 48x + 1.33x for licensing I'm not sure I could sell the bean-counters on it. :-)
But there's no way anyone here can tell you which way to go. If you can get some spec hardware in both configurations that would be ideal - you really should test your full workload cycle to see if fewer, faster processors are better for your workload - or at least close enough that they are justified by the licensing savings. On modern hardware I'd expect that to be a better option but I am not going to sign anything that guarantees it. :-)
Have never encountered anything remotely like this and suspect something has been lost in translation. I will of course apply the usual caveat for licensing questions, "don't take anything you read here as gospel, check it with your licensing partner, and Microsoft, and call both back to speak to a different individual. There's a good chance you'll get a different answer the second time around".
You get a key, you install the software. Any CPU limitation is a product of the physical environment or version of SQL Server. For standard edition that is:
Limited to lesser of 4 Sockets or 16 cores [source]
A volume license agreement is essentially a discount pricing arrangement, it does not involve a different installation, key distribution policy or CPU utilisation limitation:
If you plan to buy five or more software licenses, Microsoft offers
price advantages for volume purchasing. Discover how Microsoft Volume
Licensing can help your organisation realise its goals and find out
what customers and analysts have to say about it.
[source]
Licensing is always complex. Microsoft licensing is at least as complex as other vendors. Unfortunately, my experience has been that they have not yet mastered the art of training their own, or their resellers employees about license models.
There is much fun to be had by locking a Microsoft licensing specialist in a room with a reseller specialist and watching them argue about the finer points of SQL Server or MSDN license arrangements. If you think SQL Server is a minefield, try MSDN.
NB: The "helpful" diagram at the top of the article explaining edition compute capacity limits neatly demonstrates why folk lose their way.
Best Answer
At the risk of stating the obvious, nothing is physical in Azure as far as you are concerned. The best thing you can do is go to the Azure Pricing Calculator, find the 'SQL Server' section, select the 'Standard' section, find D-Series, select 'D4' and slide the slider to 1. That's what you will be paying, eg
SQL Server will treat that box as having 8 cores, so should you. You can also compare and contrast costs, eg try Enterprise edition. As far as running coreinfo on Azure goes, don't bother unless you've got some time to kill. By signing up to IaaS you have resolved to care much less about that kind of thing, freeing you up to concentrate on the software.
If you are concerned about performance you should cast your eye over this superb article:
Performance Guidance for SQL Server in Azure Virtual Machines
https://msdn.microsoft.com/en-us/library/azure/dn248436.aspx