If a cylinder has over .005" taper wear, or the same amount of out-of-round, it's time to rebore. The problem is that the taper wear is not linear - - - -it happens in about the top 1 1/2" of piston travel, and the rings aren't able to flex fast enough to maintain a seal on the cylinder walls. At 2000 RPM, a ring has to expand and contract 66 times a second to stay in contact with a tapered bore. Metal fatigue sets in, and the rings lose their tension and quit sealing in a very short time. A straight-wall overbored cylinder that's properly honed for quick ring seating eliminates the ring flex.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!