I had a 9x7 rigid plate on my WR for the first couple of months and then changed to a semi-flexible 8x6 which has lasted 2½ years with absolutely no problems apart from getting a bit tired and shabby but, prior to Sunday's LDT I panicked about all the discussion and put the 9x7 back on.
Big mistake - it got knocked by a mild diversion down a hedge line
and and fell, off about a mile alter. I zip tied it back on about 10 miles later only for it to fall off under it's own devices somewhere in mid Kent, never to be seen again. It was also melting because of the exhaust gases hitting it.
So I've ordered an 8x6 fully flexible plate and will possibly get a 9x7 made for the MOT in July but I have been told today by jonpaul1st that 8x6 is an allowable size on an enduro bike so I will have a chat with my friendly MOT tester and see what he can find.
I reckon only 25% of the riders on Sunday had 9x7 plates and many of those were not in great condition having been bashed about a bit.