You are correct it is perfect for Red,Sika and fallow deer and even Boar which is what I use it for but I also do a lot of hunting in different parts of the world and some dangerous game shooting so sort of wouldnt mind bringing my own double for that...
I did look into getting a set of barrells made for it in 375 but it was more expensive than the price of a good seccond hand H&H 375 double at auction.