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If you have an uncut 340 and the bores clean-up at .020 you wind up with a standard 4.06" bore which has lots and lots more piston and ring pack choices readily available. Plus you get to save the block for additional incremental bores later...If I can I go 4.06 I will and I'll save for a possible need for 4.07 down the road.

Valve shrouding is IMO more of a concern on Big block Mopar Wedges than on small blocks due the SB superior valve angle, on-center valve/bore placement, the limiting factor on SBM's is generally port cross section and pushrod pinch shrouding.

all else being equal a 340 stroker will have a bit less frictional losses at the mains due to its' smaller bearing diameter....a 360 will also be a bit heavier due to those thicker crank mains (steel is heavier than cast iron)

360s are a lot more plentiful though

As for why mopar went to a 360 instead of just a 4" bore 318 block, I suspect cost cutting with the longer 3.58 stroke allowed for cheaper but still strong cast crank production and external balancing saving millions ofver the mass production multi-year run of the engine. As evidence of that, (to my knowledge) there was never a steel or internally balanced 360 made. The 360 was also intended as a gap bridger for trucks and the big C bodys between the 318 and the (was 383, now 400).

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also thought there was a SCCA / NASCAR cubic inch rule change involved there. The 340 was always touted as the "performance engine", mostly because of when it came on board (1970)and of course the performance options available. When the 360 showed up ( 1971 - with a 2-barrel only ) the performance party was on the way out. On the market, that 340 is probably worth 2-3 times what the 360 is worth.