CCAguns,
Interesting post,... I have been a dedicated 30-06sprg shooter for decades, so I understand your interest as well. But, I have always respected European hunters opinions and their wide spread use of the 25 caliber. Over the decades I evolved to using lighter bullets in my ought6,... today, I exclusively use 130 grains at around 3,000 fps, they have been very good. The 25-06 with a 120 grain bullet is published at around 3,000fps. I don't think that is enough of a difference between the two to be concerned.
As I stated, the 25 caliber is a well used hunting caliber in Europe, and comparing the two calibers, I don't see why you couldn't be happy with the 25-06,... unless, you are more interested in heavy bullets.
Over the decades I have become a firm believer that the 30-06 ballistics can come close enough (for me) to the other 30 calibers, to NOT WARRANT making any change! I feel the same way about the 224/5.56 caliber and other 22 center fire calibers,... there is hardly enough difference (for me), that I can't reload/ballistics, and get close enough, to make any change!
Back on topic, I think if you must go 30-06, and you really like the base rifle you have, I would change out the barrel. But, if the 25-06 stock/trigger/ergonomics are NOT all that special to you, I would just buy a 30-06sprg and have both. There are some really nice entry level bolt guns on the market now,... well,... there were when I last checked, which was before this latest panic scene.
All the best!