6.5 mg/dl is definitely too high.
In addition to what DQ just said, in case there is a reason why more allopurinol might be dangerous for you, there are other drugs you could take either instead or on top of allopurinol.
Going by what you said about your tophi, you might be one of the gout sufferers who would benefit from very aggressive medication. There is evidence that having very low amounts of uric acid in one’s blood benefits people who have sizable tophi. In any case, 6.5 would be too high even if you had no tophi. Possibly it was an anomalous test result but I wouldn’t count on that.
So I would very much encourage you to broach the topic of more aggressive medication with your doctors. And don’t let them brush off your concerns!
You could also try more dietary changes but I think getting more appropriate medication should be your priority right now.