If it runs ok at 256x, then don't bother with 512.
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Cast aside your festive doylaks: dragon stuff is about to happen.
One of the biggest issues when having a hunger bar is maintaining a limited supply. In games like "The Darkest Dungeon" or "Legend of Grimrock" you spend all your time adventuring you do not have a readily accessible supply of food. Making a hunger bar a feature which needs to be managed.
In games like Minecraft, on the other hand, you have an excessive quantity of food. Where it simply becomes an annoyance you must deal with. Since it is nearly impossible to ever not have food. You can run around with a sword and kill a cow, pig, or sheep and get meat at any time.
There really is no need to answer this question. There are only a handful of 512x512 packs, presumably all of which have various lower-resolution alternatives. The in-game difference between 256x and 512x is so small that there is no reason to use a 512x. They are uncommon because there is such low demand for a CPU-hogging pack with details so minuscule, they can't even be seen.
Well my old desktop(before it went boom) could run 512x fine. 512512 packs are quite resource intensive though, I had 8gb ram 4 o whihc was allocated to MC and a pretty decent graphics card and cpu(i5 2500k and Sapphire 7850).
I have a $1500 rig and it runs it fine. I have 16gb of ram and dual 6950s 2gb each. An i5 2500k and above or amd phenom 2 1100t or fx series processor will be great especially if you plan to record. Hope this helps even if it is late