The 150/2.8 Xenotar is a great lens, I have a very late model and love it.
It is the lightest and the sharpest of all the super speed lenses (e.g.; Dallmeyer Pentac, Lee Speedic, or the Aero-Ektar). That said, it still is a heavy beast, and at f/2.8 shows some light spherical aberration, but nothing in comparison to any of its competitors. They are however pricey; $750+ on eBay in a Compur no. 2., and more in a store. The $1.5K price however is a bit ridiculous, as we would expect from L&R.