I think this is a curious, one off thread. When I've looked through this forum for 6ks comments I've found 95% unequivocal recommendations. I've bought them and been much more than happy.

5ks �1k, 5k2 �3k, 6ks �4k, 7200.2 �10k, 8k �15. 6ks stand out distinctly on this diminishing return curve, all IMHO.