Both have 4GB of RAM, a 500GB hard disk and a discrete video card.
XPS has Geforce GT 420M. Inspiron M501R has Mobility Radeon HD 550v.
XPS has Core i5-480M 2.66hz. Inspiron M501R has Phenom II Quad-Core N930 2.0Ghz.http://www.cpubenchmark.net/cpu_list.phpIntel Core i5 M 480 @ 2.67GHz = 2711AMD Phenom II N930 Quad-Core = 2524
Core i5-480M is just slightly more powerful than the Phenom II N930
Dell XPS has JBL laptop speaker set.
I could not find any review on the specific models you're looking at.
But here are some reviews on others in the same XPS 15/Inspiron M501R familiesDell XPS 15 reviewsDell Inspiron M501R