I am sorry for the delay in replying, your message missed my gaze.
I am very pleased to hear you are sailing Northern Oasis, as I am sure you know this boat was one of the three that sailed to the USSR in 1989.
So I can understand if it is a bit tired. The standard Club rig was based on a Z Spar 230 section and yes it did bend, but not break.
If you use the bigger rig then you need the next section up, the 265 (I think). You could use runners but, to be honest, personally I rarely used them. I took them off Tucanu.
You could also angle the spreaders back 15deg and fit lower shrouds. That would stiffen the rig low down. Lightweight (3mm) masthead shrouds to the existing chainplate would stiffen the top section. I fitted these to Tucanu last year.
You could always look for a second hand spar and take the fittings off your existing boat
I hope this helps