same here -- i hook my last warmup and all work sets. I was, for a while, only hooking the last workset, figuring that doing the first couple double-overhand would keep my grip strength increasing, but then I'd go to hook the heaviest workset and it would hurt more then I wanted, so I've found that hooking the last warmup and all work sets keeps my thumbs properly intimidated.
I still don't hook at all...damn I want to keep it that way.
I've done DOH singles @315. I've been doing lots of light DL volume as part of the 5/3/1 BBB stuff and have found, coincidentally, that it's strengthened my DOH grip quite a bit. I've never tried alternating grip at all... when DOH began to become a limiting factor I started using the hook. As much as people build the hook grip up as a test of manhood or something (which is silly), it works for some people and is more pain then it's worth for some. Probably a lot of it depends on hand geometry -- if you have thick thumbs, it's probably counter-productive. Donald Trump doubtless uses the hook grip.
I know Mr. B's too modest to point this out, so I'll do it for him: he DOH's 355.