The YT3000 and YT4000 are both available with 42" or 46" decks (YT3000 91728851 / 91728852; YT4000 91728856 / 91728857).
As you discovered, the 3000 has the single cylinder 21HP B&S, fender mounted speed control and no hobbs meter, while the 4000 has the V-Twin engine, pedal speed control (which requires a cruise control to hold a steady speed; fender control holds speed in any position, hence, no need for a cruise control), and includes the hobbs meter (which, if you choose a 3000 and want the hour meter, it is available from sears parts direct for $39.36 + shipping, fits into an existing opening in the dash and plugs right into an existing connector provided on the electrical harness... all of 2-3 minutes to install; really).
The V-twins are "smoother running" engines, inherent given the v-twin configuration; but the single cyl engine is not short on power nor is it a rough/vibrating engine. Most of the vibration on both of those machines is from the deck, when engaged.
The 4000 still is equipped with the Tough-Torq K46 transaxle while the 3000 was just recently switched from the Tough-Torq to a Hydro-Gear T-2 transaxle.
Sears (Husqvarna) has made running production changes to these models, which are indicated by the last digit in the model number.
The current numbers are: 288517, 288526, 288563 and 288573.
I can't opine as to how well either model will perform with a snow blade or other attachment. I believe that performance will be more related to transaxles (and how much torque they deliver to the wheels), rather than the engines (which are both decent).
Truthfully, the only way that you would determine if you prefer one model vs. the other would be to "test drive" both a 3000 and a 4000, which is almost certainly impossible because this is Sears, and not a real lawn equipment dealer (in fact, the Sears sales associates that I spoke with in the store knew very, very little about these machines, or about lawn tractors in general; this is not the "old Sears" anymore). Of course, if you buy one model and don't like it, you have 30 days to return it and order the other model, which then has it's own 30 day return period.
As regards the prices, these machines are on a "permanent sale"... However, the "deal" / bottom line price changes frequently.
The "best" pricing that I have seen is when the "sale" price calculates to approximately 20% to 25% discount from the "list" (meaningless) price.
Then Sears offers an "additional 5% off tractors over $1299.00 - Online Only" (web or phone orders).
Now that "Craftsman Club" has degenerated to what remnant Sears has left of it, and also combined it with their Sears/K-Mart "Shop Your Way Rewards" program, there are several times per year when they either offer a "special member price" or "$50.00 off" or "additional 5% off" for the Craftsman Club / SYW members (so sign up online, if you are not already enrolled).
They Frequently offer an additional 5% off if you charge the purchase to a Sears Credit Card.
Finally, the "free shipping through xx/xx/2013" is essentially permanent, as well.
These discounts are stackable. Thus, for example, I have seen the 28851 (42"/21HP) advertised for $1305, plus another 5% if you use a Sears card. About a week or so ago, the sale price, plus the Craftsman Club/SYW discount (with promotion code), plus the Sears Card discount had that machine down to a final net price of $1289.62, which I believe was the lowest price I have ever seen for that model.
So, whichever model you decide to try, watch the price (and "promotions") on the website closely.
Now the "bad" news, is that these machines are clearly built to a price point, and although they cut grass nicely, they are not heavily built, and really don't give you the sense that the machine will be with you in 20 or 25 years (probably, a much shorter lifespan).
If you read the customer reviews and the various lawnmower forums, you'll learn that the transaxles are reputed to be problematic, with many failures reported in the first few years, necessitating expensive repairs and misery. Additionally, these models suffer from a design deficiency, wherein the deck height (cutting height) is woefully too low. Everyone has to use the highest 2 positions (5 or 6); nothing lower. In fact, you cannot even lower the deck to position "1", since "2" already is in full contact with the ground (on level concrete). This flaw includes the fact that the deck mounting links are too short, and only one side of the two rear links is even adjustable. Some owners purchase a second adjustable rear link for the other side, and then drill a higher mounting hole for the front link, in order to add another 1" of deck height. Clearly, Husqvarna (and Sears) are very familiar with this engineering deficiency; they obviously don't intend to rectify it, since they have had several years to do so, if they wanted to.
I bought one of these machines a couple of months ago (replacing a 25 year old tractor), and I know that I have "rolled the dice" and am hoping for the best. Only time will tell. (But my wife tells me that "the lawn looks very nice"... )..
I hope that some of this might be helpful to you.
