What would you do with $1800?

I know there have been many threads about this, but if you are bored the advice would be nice.

I just received a grant for $1800 to buy a laptop. I have a 3 year old 13 inch Macbook pro, I am at work right now so I don't have the processor specs, but I know that I have 4gigs of ram and a 1 terabyte hard drive.

I'm a teacher so I don't do many intense things with my laptop. I watch a lot of video (I have 400gigs worth on my laptop), 100 gigs of photos, barely any music and 2000 ebooks. I randomly use iMovie (maybe twice a year).
I use my 64gb 3rd generation ipad almost all day, so my laptop only gets used when I am working on research.

So now to my decision. My laptop still works beautifully, but the grant funding has been given to me so that I use the laptop for iPad specific research. It sounds stupid, but the grant also comes with 10 ipads so they want a mac laptop to.

I am not the type to use 2 laptops so the new laptop would replace my current one. Here are my 4 choices:

New 13inch Macbook air with an i7 processor and 256gb of storage
-this means I use an external hard drive and start to depend on cloud storage.

Refurbished 13inch Macbook air with an i7 processor
-with the refurb savings I could probably afford a 512gb ssd upgrade that I would buy separately.

New 13 inch Macbook pro with an i7 processor
-I am only worried that this is not going to feel like an upgrade. I don't think I will feel the speed difference because I don't do complicated things on my laptop. I do get the hard drive storage which I like having.

Refurbished 13 inch Macbook pro with an i7 processor
-Since I probably won't notice the speed difference maybe a refurb would save some money and allow me to buy accessories.

My current Macbook pro never leaves the house because I find it so bulky compared to my iPad. Sorry this has been so long winded, but I need to spend the money by Friday and I have been so conflicted.