Increasing the size limit does affect performance, but I think you should be fine at 1000. Here's some info I found from tech support:
When objects are copied to the clipboard, only a reference to the object is copied, not the object itself. These references will use some memory, so the more objects copied to the clipboard, the more memory that will be used. However, the amount of memory that these references use is fairly small, so I doubt you’d see any noticeable impact on performance after setting the limit to 1000.