So I made a benign, interaction free sample deck on Goko and ran some games against the bot. The only kingdom cards I acquired were Rats and Upgrade. My conclusion is that the rush can possibly be pretty strong, often getting to 8 Duchies by around turn 14. Also, it is much harder to get a good balance going than you'd think. You need to empty the Rats and Upgrade piles before tearing through the Duchies. This is very doable, but you need to keep up your purchases of Copper to make a large enough deck to absorb 20 Rats. You also need to be wary of Upgrading away all of your Rats. You need to Upgrade some into Upgrades along the way, or else you'll be tossing hands full of Rats looking for Upgrades later. Also, don't be too afraid of feeding an Upgrade or two to your Rats is necessary.
So yeah, any thoughts?
12 turns(I cheated a bit, upgrading a Silver into a Silk Road)
14 turns(Here I didn't empty the Rats pile quickly enough, so I had to cannibalize a couple Duchies. Still won though.)
17 turns(This time I lose. I overdid it with Rats, not getting enough Upgrades early on, and when many turns gaining 0 or 1 Upgrades.)
14 turns(Another win for me. The balance was a little better this time, but I still stumble a bit at the end and cannibalize a lot of Upgrades. I'm realizing at this point that you need to get your deck up to 30 cards: 10 Upgrades and 20 Rats. This means I should definitely be spending spare buys on Copper, and opting to Upgrade non-Coppers to keep up my card count.)
21 turns(A loss. This time I didn't Upgrade any Rats until the Rats pile was emptied. Buying Silvers let me buy a few Upgrades, but it was not enough and I choked hard)
18 turns(Another loss. I thought it was going well, but I definitely choked towards the end. I think the spare Coppers were helpful.)
14 turns(Another win. Better balance, but a bit of stumbling.)