Like I said before I'd put my money on El G, but Geb was something special and was far tougher and trickier than Bekele or El G, so I'd give him a decent chance. The 1995-1997 Geb had friggin stupendous sprint speed, he outran Nyangabo down the stretch over 3k and hit 11.9 for his final 100m at the Goteburg 10k. Anyone who can hit sub 12 has a chance against anyone, I don't care what their mile PR is.
Also when you run the race would matter a lot.
1995: Geb kills him
1997: Geb stills wins
1999: El G wins, he is at his physical peak
2001: El G wins comfortably, Geb is nearly shot as a track runner by now.
Any date after: the race ain't worth running, El G by train wreck.
If we are talking about the best versions of them meeting:
El G should win.