I recall an article by the maker of Clearview chokes, Larry Nailon (sp?) in which he postulated that the .750 bore size was optimal for pattern performance. I can't put my finger on the article and can't recall if it was in Sporting Clays magazine or ???? Anyway, he had some supporting data backing up his claim that sounded good to me, non-expert that I am.
I have a 32" .750 bore Kolar Sporting barrel with fixed chokes of .015 and .020 weighing 1.66kg. I understand that the .750 barrels are lighter than the .740 ones, which may or may not be a benefit to you. The Stan Baker cult believed in big bore barrels but I have seen and owned a lot of .723 barrels that patterned awfully well.
Kolars, whether they be .740 or .750 come standard from the factory with more than just a large or over sized bore. They also have extra long and polished forcing cones and extended length choke tubes. It is the combination of these three things that softens recoil and improves patterns. Stan Baker was a pioneer in this field and for the longest time was criticized for his philosophies. Today, Wilkinson, Eyster and others continue his work in aftermarket form and the arms companies are incorporating his philosophies into their new guns.
The main difference as you asked between .740 and .750 Kolars is basically the weight and the ease of swing. I find the .750 bores to be far superior in this regard. I think too that my .750 bore barrels pattern a bit better and the recoil is somewhat softer than the old .740's. Many have doubted that the weight would be noticeable and it is only about 4 ounces in 32" barrels, but the proof is in the pudding or in this case in the handling of the gun. There is a difference and it is a nice one.