You can probably already do 30 reps at 90% of bodyweight, so nothing to gain there. You say you max your sustainable HR, but you don't mention your legs. Getting down in the weeds, HR is based on signals received from one's skeletal muscles. When they're low on oxygen, they message the heart to increase its rate. One of the things which increases muscle oxygen use is frequency of contraction, i.e. cadence. So try climbing in a bigger gear. Ideally, you want your legs to fail at the same time you run out of HR. You have lots of leg, maybe you need to make more use of them. Fast riders who climb at high cadence also have a high VO2max, hence doped up Lance time trialing at 110-115 cadence.
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