Interiors and tech
I will keep this short as you can get most of the info on the Ford website.
The premium trim comes with "Track apps", which are essentially functions like accelerometer, 0-60 times, quarter mile times, braking times etc. Some functions shown in below pictures.
Besides that, I have some other interesting settings. I can change the color for gauges, halo (outer gauge rings), and ambient light to almost any color I want! Ain't that full NFS style? I love it

My personal favorite combination is blue gauge with green halo (seen below).
Other functions include changing steering feel to Sport, standard, and comfort. I will talk about steering in the next section.
MyKey is a Ford specific feature that restricts driving modes like setting a speed limit, belt reminder, volume limits etc. It is similar to a parental control feature for electronics.
There is an 'AdvanceTrac' button, similar to a TC-off button in other cars. The switch allows three adjustments: traction control can be turned off; stability control can be placed in a Sport setting that allows more rear-end sliding before it activates; or both traction control and stability control can be turned off. Personally, I haven't dared to turn things off because the car is already so tail happy at corners!
Some crappy pictures of the interior:
The Mustang comes with Microsoft Sync standard. Though there are a bunch of people who have reported problems with the system, I could connect just fine with my iPhone 5. The voice command system works perfectly. The phone being in my pocket, I just have to say "bluetooth audio", and within the next 3 seconds I have music playing wireless in my car! It is as easy as that to make phone calls too. There are several other features that Sync offers but I haven't had the time to play with it much.
Driving Impressions
The engine, in one word is - Brutal! The 5.0L Coyote V8 is one of the happiest revving engines I have seen! It redlines at 7000rpm in no time. Especially since I have the higher 3.73 gear ratio (stock is 3.43), my first gear is very very short. I am at 60mph in no time! I haven't got a chance to use the track app to measure my actual 0-60mph time, but officially it should be around 4.3 seconds. That is FAST!! The main reason I went for the Mustang GT was this V8 engine. It is just spectacular and makes a deep growling noise. It is loud when you need it and muted when you are cruising. Just the perfect exhaust to ask for. Though I was still contemplating to go for the GT500 axle-backs, I have postponed that idea for now.
Coming to the handling, the Mustang has a solid rear axle as most of you would know. Theoretically, that should hamper a car's handling. But in reality, it is far better than one could expect. I think Ford has nailed it by developing a good handling sports car that a solid rear axle! I drove around a few twisty sections around Austin at about 70mph and had full control over the car. Though there were times, I thought I am gonna lost the rear but I believe it was mostly due to the damp conditions at that time. I would still not say that it handles like a dream sports car, but it is good enough and there is nothing to complain about. The strut brace under the hood really helps the car not move around a lot in corners. This brace only comes when you opt for 19inch wheels or the track package.
The steering is electric-assisted so it offers very little feedback but I really like how well it is weighted even in standard setting. Switching to the sport mode makes the steering much heavy, somewhat like the older 3 series. Perfect for high speeds and highway cruising. The car is very stable at high speeds on the highway.
A few comments about the manual gearbox on the Mustang. It is surely not the best gearbox I have used. It needs a lot of improvement by Ford and I hope they address it in the 2015 model. Though the shifts are short-throw, there is a lot of work to be done to shift through gears. Shifting to second gear is terribly hard. Other gears are still fine to shift to. I was reading on a few forums that a lot of people have trouble shifting into second. I rarely have found myself not able to shift to second, but it still is not as slick as my Polo back in India which could be shifted through gears using just two fingers. In the Mustang, you need muscles to work through the gearbox!
Again, it is just a matter of time I get used to this gearbox and it might need some work in the next scheduled service.