Texture compression artifacts on iOS

Hi all, i've got problems with the PVRTC 4-Bit texture compression on iOS. It creates many artifacts on the textures and make them look ulgy. For Android I'm using the ETC1 4-Bit texture compression and it's doing a pretty good job. What can I do to make the textures look good on iOS too? I can't go with uncompressed textures because it would kill the RAM. I'm currently using up to 140 MB of memory with uncompressed textures. What's the best practice for that? Thanks in advance. Dennis