Problem with shimmering LOWL

HiI downloaded great freeware scenery of Linz LOWL from http://www.puerstinger.net/FS/FS_DE.htmThe problem is with lot of texture shimmering.I tried to convert textures with Imagetool to dxt3 with mips.After that no shimmering, but after that size of texture folder increased for 30% and texture loading time increased.What should be the best combination, better image and smaller impact on performance.ThanksEdin