hyde, mpi's do not suck, they are good stocks....but, they will need finishing and by the time that is done you will be right near the price of a mc m. the beauty of a mc stock is they are always a good finish.....sans a few micro chips. there are a billion collor choices in mc swirlys and they never rub off. I have a mag fill on my 375H&H and would recomomend standard fill of you go the mc m route, unless you are trying to fatten the thing up. the only guns I have ever seen bust bedding were my 6.5lb 300rum and a very light 338 lapua. it would take a sub 7lb 375 before I would begin to worry about bedding issues. both are good stocks. a used mpi can fetch 250 bux, a used mc m, depending on model can bring 350-500, so resale might want to be considered.
HS stocks are pretty tough to beat for the $$. they are not as friendly to my hands and a bit heavy, but well constructed. if you like their offereings it is a good value. just do yourself a favor and never handle any mc millans as you will be stuck on them like me.