Looks like it's a 14% penalty for being 4.5 or 4 squares away. We will also lose the trade route bonus when we declare war.
Taking Machinery as an example at 1046 beakers, it takes 715.464 EP with just 5 turns and trade route.
We make 160 BPT, so that's 7 turns of commerce. We can get 132 EPT so that's 6 turns of commerce. I guess it becomes a no brainer then to try to steal these techs, as long as we don't get stalled by the 5 turns wait.
Turn 1: Cold Whip Spy in Orleans, start road on tile 1SE from NW City. Start Settler in Copper City.
Turn 2: Whip Settler in Copper City, Spy starts moving to NW
Turn 3: Spy arrives at NW, City founded on NW City.
Turn 8: Steal Machinery.
I'll finish the university in Paris, Forge in fish city, and everyone else pumping out Muskets, with Munich finishing the Barracks this turn. We'll want forges everywhere else, so I'll try to shift gear when I think we have Hatty in the bag.
Scientist specialists will be creating passive beakers. Don't want to stop working them as we still need the GS. I'm thinking Divine Right would be the best place for the beakers, since we're planning on stealing Machinery and Engineering. That would get us one more tech discount on Nationalism which we might eventually want to get for Taj Mahal and Nationhood.
Do we want Copper City to be working an engineer? We currently have Hanging Gardens, so it increases the chance of getting one, but I don't know if there are any wonders we want or techs in the GE path that we can rush. Maybe a National Epic in Thebes? It would still be useful once we can start triggering Golden Ages with Pacifism so we can speed up great people production.