I will speak to ORH. My plan is to factor in the worst for this year from an investment point and figure out how much book value could erode. Everyone is factoring in a gain for the year and following years from investments. Figure out what happens in a worst case. Figure out the implications and if you are OK with those, ORH at this price is good.
SO Ericopoly, for example, I would invert your post.
The market is down 20% or so from its highs of early this year. Start working with that instead of assuming 15% growth in stocks. Assume a combined ratio of 100% and see how much the stock market needs to collapse, assume the bond market stays firm for ORH given CDS hedges, assume the munis will payout and BRK will not be toast. So take the yield on all those bonds with no decline in value in the bonds (this may not be the most conservative from a mark-to-market as confidence in BRK would get hit - this would however be offset by the fact that the CDS hedges corp bonds and recoverables and the recoverables are not marked to market while the munis are - so call that mark-to-market issue a wash, i.e. forget this sidebar). Just take the yield on the bonds - gross them up to pre-tax. Assume they don't fall in value cause CDS would offset.
Calculate different scenarios for stock market and after-tax hit to book value. Stocks down 20% (currently the case), down 30%, down 40% down 50%. At 50%, don't forget to take 70% to get back to after-tax. If you don't like the result of the book value hit (keep in mind competitors will be destroyed at this point and a very hard-market will develop and underwriting expansion will commence for ORH), hedge yourself at whatever level you get anxious - might be reasonably cheap to do so.
I think it makes sense to do this analysis both on the upside and downside for the stock market in terms of my investment in ORH - that way, you just get pleasantly surprised, no anxiety, and all it might cost is a tad of insurance in the form of out-of-the money puts on ORH.
Analyse the upside and invert to figure out the downside to book value in a potentially very bad year. ::) ??? :P