I'm just going to be blunt and say it, you're worried about nothing. No two computers ever perform the same. There are so many variables here that there is no surprise that your computer doesn't handle the same. Let's assume you have the same exact video card as them for arguments sake (as I have yet to see a rendering program not use video cards as a main mover in strength). Do you have the same number and type of processes running in the background? same bus speed of Ram? Same motherboard chipset? Same windows updates? As Kage mentioned, the same versions of the program? One hard drive for data, another strictly for the OS and Programs? Does your hard drive has the same cache size? Same read/write speeds? Same seek times?
The more of those you answer "no" to, the bigger the performance difference between the systems. And like I said before no two systems will ever be the same. If you really want to test it, buy two dells and run the rendering before running any windows updates or installing other software. The results will be close, but never the same.