Stalker, You make a case for the Baikal but in that price range you can find a sxs used and will have a gun that
should be a lot less bulky. Try finding a used Spainish gun made in the 60's or 70's. Most won't have the english stock
rather a pistol grip. The stock on them is half the size in diameter to the Baikal.
I shoot double triggers and it took probably 2 seasons to master the decision of pulling the 2nd trigger first on wild roosters
that run and flush at 35 yards.
Another part of shooting a double not yet mentioned is the hand positioning. Your hands are closer than on a semi or pump.
This is very different at first but will absolutely give you a quicker motion when pulling up on birds.
I still pull out the 870 for the duck blind but the quick rise of an upland bird situation beckons for a double in
my opinion. I shoot mostly sxs's but the newest gun for me this year is a o/u 410. It's been fun to train with on quail.
The sight plain is different as mentioned by others on a sxs but if you get into a 20, 28, or 410 that really fits you all you really should see is the bead at the end of the gun.