Re: .257 varmint bullets
75g vmax would be your best bet, followed by the 85g ballistic tip.
The 75g vmax at 3800fps is absoluty dynamite. It literally vaporizes squirrels.
THe 85g NBT is still pretty frangible, but not as much as the 75g vmax.
You could also go with bullets like the sierra 75g HP, sierras 87g or 90g, speers 87g tnt, hornadys 87g sp.
Basically, in the 25, any bullet less then 100g is suitable for varmint hunting.
I happen to like plastic tipped bullets and thats what I mainly use, but I've tried just about every bullet there is out there in my 25's over the years.
One word of caution, a steady diet of 75's or 85's in a 25-06 isn't going to give you much barrel life. I dont shoot bullets under 100g in mine anymore. I also shoot longer distances so bigger bullets are better anyways.
I wouldn't expect more then about 1000 rounds of good barrel life shooting 75's or 85's at max loads.