The flutes are too shallow to have any beneficial effect on cooling or accurracy. The flutes only decrease the barrel sectional stiffness. It is a sales gimmick to give the barrel a superior look, and that is the only thing the flutes have going for them, looks. If you like looks it should be reserved for women.
I'm not concerned with how the flutes looks or whether or not they aid cooling. I would prefer to have the Choate stock that comes on the fluted though. The fluted ultra also weighs slightly less, which matters to me since this will be a carry gun also.
That being said, accuracy is the most important consideration to me. If a lot of people had said that the fluted ultra seemed to be less accurate than the ultra with the standard bull then I would go with the standard. So far everyone I've heard from (here and elsewhere) that's owned or fired the fluted has said accuracy is equal or better than the standard bull.
The bottom line is I'm willling to pay the extra $40 for the fluted (mostly for the stock)
if it can expected to perform at least as well as the non-fluted ultra.
The 24" bull barrel is the way to go, and in no way are you assured they will perform to varmint standard accuracy. The two I had did not.
By varmint standard accuracy I'm assuming you mean MOA or better. What kind of accuracy did you get with your ultra varmints, with what ammo and in what caliber?