Hi Jay,
I've got a set of drill bits which go up in wire gauges so very small increments. could probably do 2.6, 2.7, 2.8... Feel free to pop over for a re-drilling sometime.
(actually, you could perhaps advise on LPG tank mounting in exchange

)
25 ms injector duration will be a problem. At 6,000 RPM you have 20ms between each firing of the cylinder to get the fuel in so even if the injector is fully open it'll struggle. Have a look at the factor in the LPG map at the top end of the durations (petrol injector duration is likely to top out at about 14 - 15 ms). If it's more than 1.5 or so there's likely to be a problem. Does your LPG ecu have any "injectors fully open" faults stored?
I would try upping the pressure first, though. It's less hassle than re-drilling and reversible if it goes wrong!
Before you do, though, have a look at the vapour pressure as you step on the loud pedal (on the road, under load). It will probably briefly dip as the manifold vacuum disappears but make sure it recovers to close to the set pressure and doesn't drop off as the engine winds up. Just to make sure it's not a supply problem..
Kevin