My 9yo outlier had similar reading/language baby milestones. I'm really glad we had her tested at 6.

Schools are usually pretty conservative about testing and accommodations, so if they are suggesting testing... It sucks to have to negotiate accommodation for your dc when they are under duress. It takes forever and is nerve wracking for everyone.

Doing the testing while things are going well sounds wonderful. I would go for it!

Warning: sleep deprived