The only real analysis/simulations I've seen on this actually points to TD builds outperforming any other variant w/o TD. My guess as to why is simply that TD hits hard enough, that w/o it you can't make up the difference even with extra aim.
Assuming you don't take TD, you'll be using FB in it's place. Right off the bat, TD definitely hits for more, significantly more on crit, so that's the delta you need to make up elsewhere. Yes you can end up getting more free RS with the extra FB, but it's a 30% chance and you are only getting 1 more FB every 15 seconds, so it's not like you'll be getting a massive # of extra PPA procs.
A somewhat quick easy test (even moreso if biochem), go take some #'s on your abilities, then take a reflex stim for the aim boost. The 128 on the biochem stim is right about 9% of 1400, which is probably a fair #, give or take a bit. After taking the stim, recheck #'s and see if the increase would add up to the difference between what FB and TD hit for. (This is really a pretty huge oversimplification I admit)
I'd also add, we're not playing WoW here, no one is doing 30,000 DPS. We're seemingly in the mid 1K range. At those levels, I think fight mechanics, RNG, player skill, lag, *bugs*, whatever, matter as much as where your last 4 points go, if not more. If you get lucky in a fight with lots of PPA procs, you'll be doing very well (until you pull aggro and die ), if you use all your luck up that fight, and can't buy a PPA to save your life on next boss, you could be doing 100's of DPS less.