Rell,
A curved grip looks better than a straight grip (straight hand) on a double rifle IMO but in a medium cartridge like 9.3 I really doubt that there would be any problems associated with it.
A tightly hooked grip will indeed allow you to pull a gun in real tight to the shoulder but many 2 trigger double rifles actually have long open style grips and if you look at the hand position in relation to the grip, you'll see that the hand is really only in contact with the straightest part of the curve anyway.
My 470 has a curved open style grip.
A friend owns a 375 Flanged Mag by the same maker as my 470 but his has the straight hand stock.
I haven't fired his rifle but just throwing it quickly to the shoulder I don't notice any real difference in the feel at the grip compared to my curved grip 470.
On a medium power cartridge like the 9.3/74 or 375 fm I wouldn't knock back a double merely on the fact that it had a straight style grip.
This of course applies to 2 trigger doubles only.
Single trigger double rifles are a different story.