What do you think guys?  Having an E.A.Brown 97D rifle built in 256 Win Mag and I am leaning towards a 26" barrel to get every fps possible from the case.  Is this too long and would a 24" barrel get top velocity from this case?  Going with a 12 twist.  Need advice.  Thanks.

Alan

Alan,   I seem to recall that most ammo is factory tested in 26" labratory barrels---but that may just be an accepted standard left from earlier years.  It is also probably geared more toward velocity and pressure standards than maxamizing accuracy.
 I think the modern theory is that short and fat is better accuracy-wise.  Most of the "modern" bench guns use short heavy stiff barrels.   Longer (and heavier) may be an advantage in burning heavy charges of Black powder with heavy bullets (and soaking up the recoil), but if youre using the selection on modern powders with light bullets available they are no advantage from that standpoint. 
Longer barrels will give you a longer sight radius-----if you are using iron sights.  A number of the offhand iron sight guys at Etna green seem to be using short fat barrels with "bloop tube" extensions for increased sight radius and balance.   If you are planning on using a modern scope, shorter will work fine 
Longer barrels do "look more traditional" on a single shot but that look was developed when the sport was 90% offhand and BP or BP-like powders were what was available. On the generally shorter single shot actions even a 24" barrel looks stubby.  I guess it sort of depends on what type of shooting you anticipate---and your personal preferences in appearance and balance.

Alan
In the 70s the benchrest guys went down to 18"short and stiff. My 222R Martini is 17.5 and dosn't know it is to short. you just need enough barrel to get all the powder burned.
Tom