Sure, fly what you like; take advantage of the free perk-ride performance.
Nope. The XVI accelerates better, and its lighter weight makes up for the smaller wing area. The 2x50cals are a more effective secondary weapon than 4x303s. The XVI can also carry twice as much ordinance as the VIII, has the best low-speed roll rate in the game, and still rolls well at 400mph ias, where the VIII rolls glacially.
It accelerates 0.1 seconds faster anywhere up to 250mph. The weights are almost the same. The 8 is not heavier (100lbs last I remember), and that's WITH wing tanks.
Puh-leeeze! Let's just call it "the same!"
As far as the weapons go, the main guns have always been the uber hispanos. The 50cals are nicer than the 303s but 99.99999% of all spit drivers go home after the cannons are gone, and if they stay they know they may not get any more kills with what they have left. So, the only difference being the range (8 has wing tanks) and the roll rate.
Again, it's like the P-38L and the P-38J. One rolls better, one carries different payload, but almost across the board their speed, climb, and other charts are almost identical if overlayed on top of each other.