Thanks for the positive comments all. I was hoping this had some value.

EugeneGlock23, bonesgun is right, there is no single perfect rifle, only the one with which compromises you can live with. Like I said in one of the first paragraphs, much of this will eventually come down to personal preference. For instance, if I were in your shoes, I'd be partial to the .308 (gosh, a .30-06 owner saying THAT! Blasphemy!) fearing some meat damage from the .270. JouDoring's advice to settle for a 150gr bullet in the .270 is sound though. If you reload, going heavier or using monometal bullets will also help reduce the meat damage to acceptable levels. The heart wants what it wants so get the .270 if it speaks to you.

Tordiffe, you are (mostly) right about the parent cases. I did not include a whole host of detail on that seeing as the prospective first rifle buyer would probably not care about that info much. I only mentioned it in the 7mm Rem Mag's case to indicate the large case size relative to bullet. Incidentally, the .300 Win Mag is also based on the .375H&H. The whole Xx57 family is also essentially the same case necked up or down to fit different bullets.

The one aspect I disagree with you is the 9.3x62 being based on the .30-06. Due to the 9.3x62 being released in 1905 and the .30-06 in 1906 (from there the somewhat random "-06" bit) this is technically not possible. The 9.3x62 could be based on the predecessor of the .30-06, the .30-03. According to Wikipedia the dimensions are as near as dammit but one would have to consult a more authoritive source to check the dimensions and development history. The 9.3x62 sure looks like a .30-06 case blown out and necked to 9.3mm!

Despite not owning any myself, I also have a fascination with the metric calibres. Pity that they are not so easily obtainable as some of them, like the 7x57, is really gold. You'll certainly have to scratch around to find that 8x68 you are looking for if you do not have a gunsmith build you one. If you find two, let me know!