(more) Trouble in Paradise

Since the PowerWall install, I've been paying closer attention to my house PV production.  Normally, I look at my Curb monitoring on production as the sum of the "guerrilla" system (currently 29 ~245w panels each with an Enphase M215 microinverter) and the roof top system which is a nominal 8kw with 26 ~300w panels on a SolarEdge string inverter.  Looking at the roof top only, I was struck that there was a flat top on power vs time.  About 5kw.  So, I went out and examined the inverter.  Sure enough, "5kw".   With good sun, it looks like it is spending about 90% of the time during the best production hours pegged out at 5kw.

My experience with installers has been very poor and the one that did the SolarEdge was especially flaky.  So, I have no hope of getting the installer to fix it.  Something like "GoGreen".

Now, to decide whether the inverter is worth replacing with a more powerful one.  If so, how powerful?  I find 6kw listed but haven't seen a 8kw.

Typical "flat top" from too small an inverter: