Think for a sec of what happens in a GBB pistol and what the effect of that pressure would be.
Now I'm going to write another thread-killing essay...
1. The mag body/valves have to hold that higher pressure. I doubt the dinky little brass valves are going to hold really high pressure...you'll need to upgrade your fill and knocker valves to stainless steel.
2. The loading nozzle (thin cylinder/tube of plastic that acts as the cylinder for the piston blow back) has to contain the pressure of the gas for the pistol to operate. Operate not just once or twice...but hundreds of times, in rapid sucession. Nozzles (especially stock) crack often enough with propane...better upgrade that to the best ones you can, then buy spares and cross your fingers.
A lot of pistols are designed to run on duster or green gas. Most are just not designed with enoug space to replace parts with really beefy stuff.
3. The float valves inside the nozzles are not designed to hold in that much pressure. It doesn't happen often, but I've cracked a stainless one with propane. Buy the best you can, buy a couple of extras. And you'll need different float valve springs to balance the heavier valve and gas pressure.
4. The main knocker valve needs to hold the gas in...but the hammer spring, knocker and hammer needs to knock it open. So upgrade those parts. The hammer and mainspring rarely "break"...but knockers do. Steel ones should hold up.
5. Now here's the kicker (litterally)...you'll need to buffer the rearward force of the slide with enough power so that the slide doesn't smash the frame and itself to bits (i.e. blow right off the frame). So your frame has to be made of good material and so does your slide. Hard springs and buffers will work...you'll need to balance it. But NOTHING stops the forward movement of the slide except for the lockup points of the barrel assembly/frame...so while there's a good bit of force controlling the rearward force...that same power is going to snap the slide back forward just as hard.
6. With gas pistols, often the limiting factor is the barrel length. I've gotten 370fps w/0.20's out of a near stock hicapa on propane...but that was with a ridiculously long inner barrel. The way that the gas system works, short inner barrels do not lend themselves to high FPS with reliably working pressures. For further details on how a gas pistol works see Redwolf's pictoral write up, it's a good read.
And...that's just scratching the surface of tuning a GBB pistol.
All that's great fun...until things break. It might work one shot...or dozens. If you want to check out some wild stuff, see what the HK Airsoft IPSC guys are doing. Some of them are running HPA rigs fed into their HiCapas...don't know what pressures though. Not at all practical IMHO, but it's neat to see the limits pushed.
PS. AI adapters are great. I currently use a Madbull steel one and it works well. If I break it (most likely from dropping it), I'll try something else.