in the 25 cal rifles, I love the standard 257 Roberts, and with handloaded ammo, (with a good strong action) it can be boosted quite a bit over it's original factory loading. However, if you want more still, it makes a lot more sense to make a 25-06 than it does an "Roberts Improved"

Look at the price of the chamber reamers and the dies. Not to mention the cost of bullets and powder for fireforming.

A 25-06 and a Roberts Improved are ballistically about equal, but the 06 case usually feeds with no problem, where as the "improved" can need some action work. Again, more money spent to get nothign additional.
I have made dozens of 25-06s and about twenty 257 Roberts Improved rifles in the last 30 years as a gunsmith.
I would choose the standard 257 or the 25-06. I would have no use for the "Improved Roberts".

There's nothing wrong with it per se, but just nothing particularly right with it either.
My 2 cents worth.
SZ