MacBook – How’s battery life of the Oct 2013 Macbook Pro 15″ Retina

So there are a bunch of comments about the merit of the question which it seems you e taken the time to look at and assess. I'll jump right in to starting the discussion on upgrading.

Firstly, to be clear you're looking at a new early 2015 13" MBP (I assume you're not interested in a 15", which can support quad core processors and add a whole new layer to the discussion).

Apple's tech specs can be hard to track down, but it looks to me like you got the same processors I did. The i7 supports a turbo up to 3.1 GHz and 4 MB of cache, with the i5s boasting 2.1 and 2.7 GHz processors and 3 MB of cache. You're right in that the i7 supports VT-d, but you'll need some fairly heavy duty software to take advantage of it. The answer about VT-d is that it really depends what sort of virtualization software you're using, my guess being that unless you want to use expensive commercial software, Oracle's VirtualBox will be the first to support that (though I have no reason to expect this, or know when).

This brings us to the next level: is the i7 worth it over the i5 (will there be notable performance gains)? For you (and others with this question), probably. The increased cache, better cache coherency, and outright speed increase will be what you notice. Being that all the processors for the 13" are dual core, I was unable to find evidence that there is any significant difference between hyper threading moving up and down Intel's CPU line (unlikely, they all use the same basic core).

What you are experiencing is quite normal for MBP. It may vary quite a lot with an ambient temperature above 28 degrees C. The only inconvenience with the high speed of the fan is the noise. Rather than that, you can keep it faster and the MBP will be cooler. Obviously also the fan life will be slightely reduced but they are so performing that most probably you will not see the end of the fan life. Another trick is to make sure the MBP is placed on a surface that can dissipate temperature. A wooden table or a glass table as well as your legs are not the best heat dissipators.