Should I pay mortgage, contribute to 401K or put aside and invest

[Wakes Andre]

I contribute to my 401K around $1500 every month before taxes. The company I work for contributes around $150 to it every month as well. I'm 35 and I have a 15 years mortgage for my primary residence. If I pay the additional $1000, I pay off my mortgage within the next 7 years. If I continue to contribute to my 401K I will have more retirement money at age of 67. 

I have a dilemma should I pay an additional $1000 (after taxes), contribute $1500 (before taxes) to my 401K or just to put some money aside and buy a rental property within a few years? What are the pros and cons?