Most of what I see is strictly personal preference I suppose.
.375 Flanged Magnum sounds like a good choice for your needs. I'd recommend that you specify regulation with current Kynoch rather than Romey. Holland uses both. I had a really nasty experience with the Romey in a double, and have heard of others. I'll never trust it again.
26" barrels on a double rifle are already really short. Nothing is gained in handling by going shorter, and velocity is lost.
One standing for 50 and one folding for 100 for a .375 Magnum strikes me as odd. I use 100 and 200 on doubles chambered for cartridges that don't shoot as flat and really like that combination. I've never found a need for a 50 yard leaf. 100 and 200 is ideal for a .375.
I vastly prefer the claw to Holland's proprietary mount. I know, it ain't Holland, but if you're going to hunt with it.....you're already departing from tradition with the palm swell anyway.
You'll probably get away with the beavertail on a .375, but why take the chance on something you're going to use on dangerous game? A failed solder joint on the fore-end loop leaves you with a club, and that's more common with beavertails on DRs. On a double rifle, if a beavertail is protecting your fingers from the hot barrels, you're not holding it correctly anyway.
Congratulations on your new rifle. I'm sure you're excited. Patrick seems like a nice guy. I'll bet HE'S happy.
