Subject: Re: BRK.b 1.674 x book
"In an untaxed account, selling know and buying then would get you a one time return of 10%, minus however much the value of a share rises in the time it takes to reach that valuation level. Not exactly a life changer."

It's the 10%, minus any increase in rise in value (measured by book) prior to being able to pull the trigger, plus the money earned on the cash while you wait for the purchase. The return on cash can get you beyond the 10% return or otherwise mitigates the issue of rising book eating into the return (or turning the trade negative).

If Q4 book is the peak book for a spell, and you get a 10% return round trip at the six month mark, while having a 5% (before inflation) return on your cash, it's a 12.5% return. Still not life changing, but not nothing either.