The Thinkpad e540 is about $50 more than the Thinkpad e545. (Around $550 on Lenovo webiste (e545) vs. $600 on Amazon (e540).
I really couldn't care less about the hard disk because its almost impossible for me to even fully use to 320GB Hard Drive. As a student I mainly use CAD programs, Graphical Rendering, some programming and occasionally some Battlefield 4 (I don't mind the integrated graphics)
Going on CPUBoss looking on various benchmarks I do notice that the 4200M is somewhat faster than the AMD a10 5750M (Even though the 5750m is currently one of the best AMD mobile processors). However, looking I find that benchmarks for the intel hd 4600 (such as 3d mark, etc.) show how the preformance of the integrated AMD Radeon 8650g is somewhat better than the Intel HD 4600.
Mainly, I question whether I should get the slightly more expensive laptop with the Intel I5 or the slightly cheaper laptop with the AMD A10.
its your choice. both would be fine for CAD and such. if you plan on using them for gaming you need to find a better option (one with a discrete video card which is closer to desktop video card as it wont share system ram to run the gpu) My amd a8 laptop has a discrete radon with 2gb ddr5 ram for it built into the motherboard (so i run cross fire to run games) to bad video card on laptops cant be upgrade anymore so remember what you buy u will be stuck with. (fyi im an amd fanboy so im amd all the way but the intel would be faster on the cad programs and programming compiling. i belive graphical rendering will depend on what program as amd could be better there.
I don't think it will make a huge difference, they are both twin CPU systems (i5 has 2 CPU's with 2 threads per CPU). The main point is to get something with good ergonomics, i.e. whichever one has the better display, and scratchpad. You might get the A8 or even A10 model from Amazon if you care to search for it, the A10 has a quad CPU and costs only a little bit extra.
In the area of the scratchpad, there is NO QUESTION AT ALL that the e545 has a highly superior scratchpad with real buttons, the same one that is descended from the Thinkpad 700 in 1995. The e540 has the very mediocre imitation of the very mediocre apple scratchpad (but it lookz cuil, sayz steve jobz!)
Get the e545 for the scatchpad, you won't regret it, you will save a great deal of time in college and will have more time for a girlfriend and to attend parties ...