It depends on which schools you're aiming for. A 158 will get you into a lot of quality schools. If you're aiming for schools with a median lsat in the low-mid 160's, then you should retake. You might be at a slim disadvantage, but if you indicate on your applications that you're taking the dec. lsat, most schools will hold off on making a decision. If your 158 is within their LSAT range, then you'll probably get accepted anyway. Again, it's difficult to tell without knowing your other stats and which schools you're targetting.