Actually if you back is fried after 4-5 days than your may be doing something wrong with that 5X5 scheme. 5X5's have been one of my favorite, and many other people, standard workout cycles. You back should feel well worked after a day, at the most two, but return back to normal and ready for another 5X5 session that same workout week. Even when doing extra heavy power rack training you should not still feel fried 4 or 5 days later. I know everyone responds differently to training but normal recovery should not take that long. No malice intended, just an observation. Good Luck.