I remember we had it working with way more than 60MHZ., during the 4.0 beta test.
But I can't remember what speed it was, and I tested with an ILI9341 which may have been the limiting factor. And i did not have the right instruments to measure these speeds.
I can remember - in theory - there are even settings above 100MHz possible (which involves switching to an other PLL). I have no Idea if that would work, though.
I took a very brief look at the data sheet - seems that the chip is a bit picky about timings. That could also make it difficult. So I would first take a close look at the data sheet.