I believe the pack you found is actually called the Guide, not the Mountain Guide. It’s a day pack that weighs two pounds, five ounces, which of course is quite a bit less than the Reality (four pounds, 15 ounces). It also has much less capacity — 2,400 cubic inches, as opposed to 4,350. That’s also why it costs a lot less than the Reality: $89 versus $230. And while this isn’t a knock on the Guide – it’s a nice little pack — I don’t think you’ll find room in it for much overnight gear no matter how efficiently you pack. Also, while 30 pounds isn’t a heavy load, the Guide’s suspension will barely handle it, while the Reality will support it (and more) with relative ease.
So I think you still have some shopping to do, though you’d probably be perfectly happy with the Reality. While not a featherweight pack, it’s sized very nicely and has a suspension that makes a good-sized load feel lighter, which is what a pack is supposed to do. Or, in the Mountainsmith line, take a look on that company’s new Auspex ($259). It has Mountainsmith’s lightweight (but still very good) Specter suspension, and 4,200 cubic inches of capacity, which is plenty for efficiently packed supplies for a three- or four-day trip. It weighs three pounds, seven ounces, which at a pound and a half less than the Reality might well make it worthwhile to spend the extra $29.