1) any store worth anything should let you demo any club before you buy so the biggest thing is to try them out before you buy

2) 4 degrees may not seem like a big difference, but the typical 56 degree wedge and 60 degree wedge are made for very different purposes. Most 56 degree wedges are sand wedges, and are built for sand. They will have a large lump of metal under the leading edge -- this is termed the "bounce" of the club -- and it there so that the club doesn't dig too deep into the sand when hitting sand shots. This lump acts fairly similarly to an airplane wing and helps the club just slide through the top layer of the sand. Comparatively, most 60 degree "lob" wedges will be built with very low bounce so that the clubhead can slip between the ball and the ground. If it had high bounce like the SW, the bottom of the club may strike the ground and bounce up and the ball gets hit with the leading edge ("skulling" or "blading" it) instead of the lofted part.

So, this kind of comes down to what the course(s) you usually play are like. If you are in the sand a lot, and especially if it is light and fluffy sand, this isn't really a question, you need a SW. On the flip side, if your home course doesn't have many or any bunkers, or the sand is usually hard and compacted, you may like a LW better because you can usually pick the ball off the sand in those conditions.

3) 60 degree wedges were not common until recently (15 years or so). For a very long time, the highest lofted wedge anybody carried was 56 degrees. You can always open the SW face up to increase the loft and hit those same high shots that you can with a LW.

4) There are compromise clubs out there -- like a 58 degree wedge. You can choose to get a 58 degree in high bounce or low bounce. Or even with grinds that are high bounce on one side of the club and low bounce on the other.

(Probably didn't think it was this complicated, did ya?)

5) This is a big one in my opinion. How many degrees of loft is your PW? Because what may ultimately be the best is to get a wedge between your PW and your cheapie LW.

6) Lastly, is there something wrong with your LW? You don't necessarily have to replace it just to replace it. Especially if you don't have a SW already. Having a club for the sand is pretty much 100% a necessity, especially if you start playing course with lots of traps.