RE: Need advice on calibers.
the (.30) in 30-06 actually specifies the bore diameter, not the bullet diameter.
A .30 rifle such as .30-30, .30-06, .308, .300WM, etc, has a .300" bore and generally has the rifling cut .004" deep for a .308" sized bullet.
The 6.5x55 is a very good medium sized game cartridge IMHO, The old Swedish military rifles have a very fast rifling twist allowing them to shoot bullets up to 160 gr very accurately. I have a few of the M96 rifles which make excellent target rifles- being more accurate and better made on average than most production rifles today, but they are way to long and heavy for hunting unless you are hunting over open fields.