I've had a 28T oval ring on my MTB for the last 8 years. It's very helpful to allow for recovery during non-technical climbing, but for tech climbing I generally need to upshift a a gear or two to get enough thrust to get over obstacles. I do find that I spin out in the 28/10 top gear - most often when on pavement while heading to/from trails - but this is a small price to pay for greater climbing endurance.