HST are nice and convenient. I've run both in many forms, but nothing that would compare to one another. I can say, that I do prefer the gear tractor over HST. I get a gas peddle, which for me, is nice when doing quick operations, like FEL work or moving things around the yard. The tractor 'idles' (high idle, around 1500rmp due to DPF garbage) when not doing the actual work. I do know there are tractors with a smart/synchronized HST peddle option that will rev up the engine more as your press down more on the go button. See the new LS MT3 series. I am sure there are many more like it.
Also, the HST models have extra filters, which is more money and more of a pain in the long run. Not to mention that buying new, HST are typically more expensive.
But for me, I'd drive an HST, but prefer a gear. And that, I think, is the crutch of the issue: what do you prefer?
That does not address the OP's question though. He wanted to know which tractor would pull better. I dont have a good side-by-side comparison to offer. But driving a gear tractor doing field work is much nicer.. for me. YMMV