i'm no shrinking violet: 6'2" and 225 lbs. i suggest you definately stay away from the rogers and spencer for your first choice (see my email today). i cannot get a decent grip on that design.
the walker is a very large pistol and you may find it way to heavy to shoot regularly unless you have a grip like a bear and the endurance to wave almost six pounds of pistol around. also, the walkers have a characteristic of dropping the loading lever under recoil. slows down the shooting time (a walker calls for 50+ grains of powder - that's a rifle load!).
i suggest the .44 remington. it's comfortable and use proven. the colt's are the best looking but i like a top strap pistol.
good luck, geo.