A Single Mod Resource Pack, Causing Such Performance Issues?

[sonicboom282]

So, I play the Vanilla+ pack on FTB, and have a lot of fun with it. I also run a few additional mods on the side that I added myself (things like Mystcraft, Thaumcraft, and Biomes O' Plenty, etc.), but nothing too technical.
I use the Sphax PureBDcraft resource pack, with the additional resource packs on the proper sizes, so that everything has the same resolution and look. Everything runs great, it's awesome.

Now, the other day, I thought it'd be fun to mix things up a bit, and so I decided to add Tinker's Construct into the mix. It's a mod I've used before in much larger, and more complex packs.
Installed it, ran my game, and everything was fine. No performance hits, all the blocks were appearing on NEI just fine, everything was working. But I realize, I should install the Sphax resource pack, so that it all looks the part with the rest of the pack. So I do. Next thing I know, I go from an average of 120 FPS, to 6. So I uninstall the resource pack, and it goes back to normal. Confused, I try moving it in the load order of packs to see if it affects performance. Surprisingly, the further up I move it, the better my performance becomes, and at the top, I get about 20-30 FPS on average (though it chops like mad, reducing the actual visible Frames to about 10 per second or so).

Long story short, I simply don't understand how a single resource pack could be lagging everything so badly. I'm running the latest stable 1.7.10 build of Tinkers, and am using the proper resource pack, and have even tried different versions of both the mod, and the resource pack, but to no avail.

What exactly is going on here? And how could a single resource pack, out of the 20+ I'm already running, cause so much unearthly lag?

Thanks so much for any input, thoughts, and/or solutions.

[ChaoGirDja]

Well...
There is some Point, at witch you RAM/vRam is full"
Tinkers is an Mod with many many Textures. Adding it's Resourcepack in an other Resolution then 8Bit (the Default) means, adding much much big Textures.
The 64x-Version of Sphax-Tinkers is ~24 MB large...
This is one of the biggest Texture-Packs i have come across.
And the biggest in relation of the Mod-Content (Tinkers don't add much functionality).

Long Story, short meaning:
It is not Surprising, that this Texture-pack had an big Impact on performance. Because it is an big one.