I'd stick with some 150gr bullets out of your 308. I'd sight in 2" high at 100 yards. I'd use some Nosler Ballistic tips as well.

I shot my first pronghorn a few years back with a 140gr Nosler AccuBond out of a 7mm Rem Mag, it made a mess out of it. This fall I will be toting my 25WSSM.