550s will be near out of duty cycle at 350whp. It has been discussed here many times. 1000s on the other hand, on my car, max datalogged value was at 50% duty cycle. However, it is worth noting that duty cycle increases under load at lower rpms, so I max my 1000cs on the street at low rpm and as boost comes on they back down on duty cycle. My 1000s at 350hp ran smooth as silk and now that I am dishing out more hp I am glad I bought the right injectors once and don't have to upgrade now.
I say deck the head and do the right head gasket based on target compression ratio. I currently have running a 0.8mm HG, since I have low compression Greddy pistons
