Just check Apple website. Their 13" MBP only offers Core-i5 Intel processors. So it seems it's a non-issue if you buying a new mac.
If you're a student, you'd be new to most architecture projects assigned to you, meaning that you would be spending more time thinking than turning the crank (drawing, scaling, shading and searching for pallets, etc), so you are unlikely to tax the processor power of the Core-i5 probably until your fourth or fifth year in school. For most workstation-like applications, it's not often that the application need to spin off four different tasks to perform the action you take in the app and keep all four processors of the Core-i7 quad-cores (4 processors) gainfully employed. However, whatever task you're doing, you need that one task to complete quickly. i.e. No spinning pinwheels. So a higher speed dual-core processor is better for you than a lower-speed quad-core processor. That said, there are reason you may want to consider a 15" MBP if you can swing another $500.
I personally use a 13" MBP with 2560x1600 screen resolution, but mostly for portability. I also do not do architectural graphics nor use Photoshop more than 2 to 3 times a year. If you expect to do a lot of exact graphics work on your computer, shirt of a desktop with at least a 1920x1080 screen, I'd go for the 15" MBP because it gives you a maximum 2880-by-1800 screen resolution, instead of 2560x1600 screen resolution on the 13" MBP. This means you will do less scrolling around (at human speed) on your desktop when working with graphics and photos.
The 15"MBP has 16GB memory vs 8GB on the 13". While a large project that help fill up the 8GB memory on the 13" and have to go to the much slower SSD to get the additional data, that is unlikely to happen on your 15".
Your professor or TAs should be able to give you their experiences on the sizes of your projects and what they wish they had more off.
In case you're consider buying older MBPs, here are the trade-offs you should consider, in their order of importance:
1. Screen resolution. Choose larger to minimize scrolling at human speed.
2. Graphics processor speed. Choose faster to avoid spinning pinwheel when doing stuff like rotating 3-D house plans or adding shading.
3. Memory size (8GB on 13"; 16 on 15") is a consideration if your project are large enough that upperclass students with old laptops equipped with HDD see the disk light come on when they already had 8GB memory.
4. Storage speed: SSD is much better than HDD, but it's something you may be able to upgrade yourself with some expert help. Non-issue on recent MBPs or new ones.
5. Larger L3 cache
6. Faster processor
With MacBooks, the choice are smaller and easier. The models with faster process speed comes with a larger L3 cache too.