Originally posted by skierd Once I opened the files in Lightroom, they were noticeably better than what I get from my K-30 in terms of noise and overall IQ, even compared to the higher end Pentax lenses I have now or have rented
"Noticeably better" is a little vague. I see a lot of medium to large sized prints from FF cameras. I'm only seeing differences in some of the larger prints, and even then, it's not always blindingly obvious. For landscape photography, the main advantage of FF over APS-C is FF has a built-in resolution advantage due to the larger sensor. However, that resolution advantage is not as large as some people think. It tends to only be noticeable in larger prints and/or bigger crops, and even then it may take a sharp eye to really appreciate it.
If you're going to move from APS-C to FF, it seems to me you need to decide what you're trying to gain from it and then make choices that will maximize that gain. If you're looking to gain resolution, a high MP FF camera like the D810 might be a better choice. If it's high ISO performance you're after, then you'll need to get lenses that are at least as fast as what you have for APS-C, because if you give up a stop with the FF lenses, you'll be throwing away the lion's share of the FF high ISO advantage.
As for wildlife shooting, I still think APS-C tends to have an advantage here, at least in terms of price. Sure, a lens like the Nikkor 200-400 f4, shot on an FF camera, will "out perform" (but only in terms of resolution) the DA* 60-250; but that Nikkor lens is nearly six times as expensive and three times as heavy as the 60-250. As for the Tamron 150-600, while that's a nice enough consumer grade super tele zoom, especially when shot on FF, at equivalent focal lengths, I would expect you would get better results (if not in terms of resolution, certainly in terms of contrast, color and overall rendering) with the DA* 60-250, the DA* 300 or the DA 150-450 shot on a Pentax APS-C camera.