Vienna Gambit accepted

I am a e4 player, and if my opponent replies 2... e5, I always follow up with 3. Nc3 - the Vienna Game. Here my opponent can reply in several ways. The most natural response is 3... Nf6, which tends to come up in at least one third of my games. If I am in mood for a positional game I will now do 4. g3 with the plan to fianchetto on the king side. For a sharper game there is 4. f4 entering the Vienna Gambit. The correct response for black here is 4... d5 and the plan 5. fxe5 Nxe4, but few players at my level know how to play against the Vienna. In practical play it is very rare that I see this move. Instead I often see 4... d6, 4... Nc6 or, after a long silent pause, 4... exf4 - the position below. This leads to a very difficult game for black. Usually he is unable to recover from the loss of tempo.