Since this is your ONLY 9mm handgun, you may be able to slowly work up beyond max data, particularly with those specific cast bullet loads that are well below 35K psi at the max book charge. Just beware of shooting same reloads in a "lesser" pistol.
Take calipers and measure the web of your fired cases. If your cases start to bulge too much, you have run out of room to play. Unless you want your brass to be one-time-use, only. (Bulge busting shouldn't be done, regularly. If your load is bulging brass that bad, you are best off tossing the brass. And it doesn't work too well with the tapered 9mm cases, although it can supposedly be done with the Lee 9mm makarov FCD.)
Your gun is optimized for a higher recoilling round. Since you are a handloader, you can give your gun what it wants. Just keep an eye on brass/pressure. Load 'em as long as can fit. Choose bullet and powder, wisely. In all likelihood, you can work up a cast bullet load that doesn't even exceed max pressure, but which will cycle your gun with plenty of authority - but which could cause excessive recoil and failure-to-extract malfunctions in regular 9mm's. Recoil/cycling speed is the reason max load data (particularly with cast bullets) is often capped well below max SAAMI pressure; your gun has more mass than the stock 40SW configuration, even, considering the conversion barrel is heavier than the stock 40 barrel. In other words, if you have any interest in working up a 9mm major load, you have a pretty good platform in your hands.
If this doesn't make 100% complete sense to you, and you're not 100% comfortable with the implications, chalk it up as bad and dangerous advice. Disregard and stick to the books. But if you want a round that cycles your specific gun faster than stock ammo, you do not necessarily need higher than normal pressure. But you do need higher bullet momentum than normal book loads.
