Lets look at this logically. Any bottle neck cartridge is designed by constricting the bore diameter to increase pressure, and for a longer time, therefore increasing velocity. The more constriction, the higher the pressure needs to be. That is why they refer to "overbore" cartridges, such as the ultra mags, weatherbys etc. There is a specific relationship between bore, barrel length, and powder capacity, any time you adjust one, they all must be accounted for. If you increase the powder charge, you must make it slower or risk dangerous pressures, or you can increase the bore diameter. If you shorten the barrel, you must increase the burn rate of the powder to use it within the barrel length. Therefore, to use a short barrel efficiently you must use a medium to small capacity case, and if you want a higher velocity bullet, a larger bore. For example, try shooting a 150 gr 7mm bullet from a 7mm08 with an 18 " barrel, check pressure and velocity. Now, take the same case, a 308 variant, neck it up and shoot a 158 gr 357 bullet in a 358 winchester, same barrel lenght, and look at the specs. That is why in short barrels larger bore in relation to case capacity is usually better, together with medium charges of faster burning powder. Given your options, the 30/30 looks best.
