Last time I was at SP their compressor only runs up to 3000psi, and depending on how fast they filled it the pressure would drop back a bit as it cools. And remember that the minigauges on paintball regs are often not very accurate.
Your best bet if you're not happy with the fill pressure is to phone around the dive shops in your area for one that has a 300bar compressor, and leave the tanks with them for an afternoon so they can fill them gently, so the pressure dropoff is lower.
If you can afford 2 tanks it makes the air you have go further, by keeping the pressure higher in one tank by only "topping up" from that one.
Your best bet is to phone around the dive shops in your aread for one that has a 300bar compressor, and leave the tanks with them for an afternoon so they can fill them gently, so the pressure dropoff is lower.