Yes, I do have dual high pressure 255's (in tank) on the turbo car. Thought about doing that, but don't really need that much capacity and it's going to be a lot more involved than just swapping the existing pump. Using the dual pumps also required remote mounting of the fill level sender/float and now the readings on the gas gauge are always a little screwy.
On my 91 I'm currently using a KB boost-a-pump, 6AN braided steel supply line, billet high flow fuel rails and a remoted mounted Aeromotive adjustable regulator plumbed with 6AN socketless hose. Return line is stock. If switching to duals I'll need a 2nd 6AN supply line, and a 6AN return line to handle the additional fuel flow. I would also need to re-plumb how fuel is being supplied to the rails.
If I could get another 15-20% of capacity from a larger pump, that should be plenty and won't require any other upgrades to my current fuel system, except for a fuel pump wiring upgrade. I'm just not sure the 310 lph focus pump will flow as much fuel as the 255 high pressure unit does above 60 psi. I'm still looking for some performance data on the Focus pump vs. the 255 High Pressure before deciding what to do.
David