This is a familiar story. I was the same re allopurinol. I stopped but a few years later I developed sub-acute gout. Almost constant low level pain with some acute episodes. Fact is you’ll need to be in some for of UA lowering therapy at some point.
Regarding dosage, your originally quite high UA level would suggest 300mg is a decent dose and UA level of 300 is better than 350. Also from a practical aspect a single 300mg allopurinol tablet a day is easier to manage with a busy lifestyle.
There is evid nice if breakthrough attacks with initial dosage increases but this indicates UA lowering therapy is working. Crystals breaking up shed their protein ciast and reexpose themselves to your immune system, hence the flares. My advice is to see a rheumatologist. They are experts in this field and their experience is invaluable.
Btw I’m a clinical biochemist and I thought I’d handle my gout alone, I still do my own bloods but clinical input is very helpful.