Matty, the bonus the Vortek conversion has is that is is essentially still a synthetic seal, so it gives the soft shot feel such seals give BUT if flies faster as an O ring is doing the sealing with less friction. So, you gain power and you gain the soft shot feel...so it usually is a win win using them.

Plus on the 55 the old seal is 11mm tall, the new seal you are using is 6mm tall, so you gain around 5mm stroke, which is enough to push the gun to 10fpe with out having to use a harsh spring. My 55 is so easy to cock it feels like it would never do 6fpe never mind 10.5fpe.

O rings are fine, as long as the transfer port is small enough to allow piston braking but large enough to allow good flow.