haypers This is an old thread and the Construct Team doesn't really like us replying on old topics unless it's really related to the OP.
Anyway, regarding your question. Yes, setting them off-screen or invisible does improve performance and the canvas doesn't draw them, an exception is by setting the opacity to 0, which still draws on the canvas and does consume resources.
Create / Destroy actually uses up more performance compared to re-using instances. But fortunately, the c2runtime especially the c3runtime supposedly has a pooling system which reuses instances, that's why bullet-hell games don't have a huge performance impact and are optimized, in the basic form.
A side-tip, disabling events by Groups, on the CPU-side, can give a huge performance improvement. Especially events that are not triggers (green arrow conditions), such as Every Tick condition events.
Using functions / trigger events when necessary compared to just using toggle every-tick condition events, can be a huge performance improvement too.
I hope that enlightened you in the subject.