Whack the B tension screw in as far as it goes, I find this reduces chain drop by making the mech springs work a wee bit bit harder. Make sure the ring is aligned with middle rear cog as closely as possible and do run the chain as short as possible!
Short cage mechs work better; if using up to 28 or even 30 tooth bottom gear you can just get away with a road mech (eg shortest cage 105), if using a 32-34 use a s/cage MTB mech. Of course, this is just what's worked for me
You can even botch a front mech in fixed position (using High and Low screws) to help reduce chain drop but it's only ever been an issue to me when I haven't done all the above, and then only off-road.
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vintage Brooks Professional saddle | Specialized FACT CX fork | Columbus fork | Reynolds 531 fork | Avid Arch Rival v-brakes | various 700c, 27" and 26" wheels | vintage Weco hubs (fixed/freewheel) | vintage Raleigh ladies frames + lots more!