Maybe, maybe not. To upgrade your processor, the new processor must be socket AND BIOS compatible.
Here are your two processors: ARK | Compare Intel® Products
So, you will have to contact ASUS and ask them what processors are compatible with their bios for your X71SL. Then, you can select from those processors.
Also, I have a very foggy memory of one of them (they are from two different families) not fitting the socket properly (or something like that). I could be mistaken. However, your best approach is to have ASUS provide you with processors that are BIOS compatible.