Please check out my portfolio, 2008 Have a portfolio you'd like critiques on? Or simply want to have a place for you to put your portfolio for possible employers to view? Than this is the thread for you! No longer will we be keeping individual threads on portfolio pimps in the P&P forum, we'll be slowly migrating them in…
I'd say that if you can't tell much from a level design / game design portfolio, then it's not a well designed portfolio (a nail in the coffin of a designer). A good design portfolio needs to communicate to the viewer what they are looking at, and why. It's not really so indistinct from the actual level / game design…
Honestly if this is for a portfolio piece just go as high as your PC can handle. Quality is king for portfolio pieces and you can always shrink the texture down if you find it unreasonable.