Over the last few years, the Store Merge tool has come under some criticism. We've responded with an update (it's in preview for 7.4.1) this summer. Here's a shot of the old merge tool, after selecting package HTTP:

Now, notice how it's offering to merge just about every version ever published? It also took forever for that list to pop from the DB. With the new tool, that list pops immediately, and it looks like this:

Notice how I can easily select the packages to merge? Now, here's what it looks like after I select 3 of the versions:

Much nicer. Load it from preview and take it for a spin.