You know, 33,000 is alot on the clock for a high compression sport bike. Some of the aces had slight faults in the bore that allowed for a slight loss of oil, but at the very most I have heard was approximatley a quart between changes. If you are burning enough for the oil light to come on every 300 miles, then I would say at the very least your bike needs honed and ringed. Get a compression check done on the bike, that will tell the whole tale.
Also, the discussions go on and on about motor oils. But the Ace has a wet clutch. 10w 40 , even a synthetic 10w 40 is a pretty thin oil at the temps the Thunderace reaches. Yamaha spends millions of dollars researching their products... testing and testing some more. They developed Yamalube for a reason, it has quite a few additives that reduce wear and extend engine life, as well as protect the clutch. They spent alot of money developing things like the exup, TPS, aero dynamics, and the YZF engine. You can bet the house they spent a lot of time and money researching what oil and additives offer the best lubrication and protection for their motors. The recommended oil for the Ace is 20W 40 Yamalube... just as a personal preferrence I tend to stick with that.