I figured I would chime in on what I have experienced with some of these rods mentioned...
Considering that you already have the 7'9" 5wt. I personally would think twice about purchasing any of these 3wts. that you mentioned for several reasons. I own and fish the 7'9" 5wt. as well and find that it does a great job in the park and is actually a pretty fun sensitive little rod even on smaller fish. Yet for really being just a dry fly rod it remains somewhat versatile being able to toss a little weight or small streamer if needed. However, I thought as you did and felt I "needed" a lighter rod so I bought the 7'9" 4wt. as well. I am still mixed on how I feel about it. I think the finesse are great rods with a #14 Adams on the end of the line and you would be hard pressed to find one better in the same price range. If you are looking for a strictly dry fly 3wt. then knock yourself out as this is clearly the best choice IMHO. I know a lot of people who rave about the smaller 3wt.
Now, what I would recommend is following what Buzz did and check out the 8'9" 3wt. Since you already have a short rod that packs down for the backcountry, I say go for some length but then again, I like long rods in the mountains. Similar to Buzz, my go to rod in the park is the 8'9" 4wt. finesse because I just like the versatility of the 4wt. and the extra 12".
I have thrown the BVK and it really puts out some line. Much more capable as an all around stick then the finesse but it's definitely a faster rod and would depend on what kind of feel you are looking for in a 3wt. From my arsenal of rods listed you can see it's not really my cup of tea...
No exp. with the Echo but hear good things about it.
Tight Lines,