I'd say it definitely has a noticeable affect on frames. I can run 16x resource packs (default, and similar) at ~100 frames on average and I normally maintain this up until 128x. I start to lose some frames with 128x and 256x, but each are still very playable for me at around ~70 fps. 512x though... I don't see why you'd need a 512 texture pack anyway, (256x is PLENTY in my opinion) but you'd need quite the beefy computer for sure. 512 knocks me down to 30 or less, and I've got a decent build.
Another tip I'd add though, is that if you're looking for a high-res pack, hands-down use optifine instead of mcpatcher. Optifine adds all the bells and whistles in-game and also supports high resolution packs as I'm sure you know.