Barrel length
I think velocity gains over a 26inch barrel would be relatively small possibly less than 100ft per second. If it were me I would go with 26inches which is what most of the reloading manuals base their data on. I guess you are talking a range gun as 28 inches would be a bit tiring to carry out in the field.
A few years ago I gave one of the young guys at work some advice which he chose to ignore when he bought a 30 cal winchester Magnum and was talking about cutting the barrel down to 20inches. It was a very nice Mauser rifle but against my advice he decided to cut the barrel down. First thing was groups suddenly went from 3/4 inch to 1 1/2 inch and the worst thing was the increase in noise and muzzle flash. He realised he had made a mistake but you can't glue it back on once you have cut it off. He went to about three different smiths to get that rifle to shoot better but it was a lemon. He eventually tried to sell it but nobody was interested in it. I eventually took it off his hands for the equivalent of $200 usd it now has a new MAB match barrel and regularly produces five shot groups around Half inch. That guy lost over $350usd on that rifle.
