Very useful - however, I think that the speed EVs are missing the most important training spot(s) of all: virtually any body of water with a high rate of encountering poliwhirls and poliwags. While keeping track of information like this in notepad and looking up specific encounter rates, here's what I came up with. Unedited, so it's a bit messy; I didn't intend for anyone to read it but myself until I saw this topic. The below information on encountering poliwhirls and poliwags assumes that the player is fishing, not surfing, at the pond closest to the Viridian City pokemon center, and that they're using a super rod. A good rod decreases the total number of combined poliwhirl/poliwag encounters from 80% to 60%, making it a worse choice.
Speed EV training - Poliwhirls 2, poliwags 1, found only with super rod, Viridian City pond 5 steps from pokecenter = best spot, 40% poliwhirls, 40% poliwags, 15% gyarados, 2.5% psyducks and 2.5% slowpokes. IGNORE slowpokes, but DO DEFEAT psyducks, 1 sp. att. EV, may as well.
Breakdown:
40% 1 EV (Poliwags)
40% 2 EVs (Poliwhirls)
20% Null (All other pokemon)
Total average of 10 encounters: 12 EVs (4 EVs from 4 poliwags, 8 EVs from 4 poliwhirls)
^ With macho brace: 24 EVs, obviously
Speed EV training 2 - Dugtrios 2, digletts 1, Diglett's Cave, great spot since there's only Diglett and Dugtrio
Breakdown:
95% 1 EV
5% 2 EVs
Total average of 10 encounters: 10 EVs (10 EVs from 10 digletts, negligible EVs from dugtrio)
^ With macho brace: 20 EVs, obviously
And, of course, the longer you train in either spot, the more noticeable the gap between the EVs you gain in each location becomes.
I hope this helped!