I'd go with the Vortek tuned gun. I have a .177 34 with wood stock, did the Vortek tune myself, and I'd say it's well worth what you pay for it. Vortek's price is very reasonable for a new rifle plus kit, and the Vortek kit lives up to it's hype.
If you do decide to buy a stock rifle, bear in mind that they ship almost bone dry. I've owned several Diana's, with the exception of one that was tuned when I got it, they were all dry. One of them had been shot enough that the piston had galled the compression tube pretty badly, and the innards were all full of metal dust. Makes me wonder what the inside of rifles like Jeff's looks like, sorry Jeff. Later.
Dave