From another perspective - the recent Mountain Run some of us did last week:
Shortly before doing the run, I had a chance to experience Brett's 350 LT5 thru (4.10s). There is NO QUESTION the seat of the pants could feel the increase in punch over my 3.45 cog (allowing a little to maybe an extra ≈ 30 hp for the bigger cams in Brett's car).
But, as others have said, 6th gear in the mountains was pretty much useless, except above 70 on flat stretches. I believe a bigger ratio would have been useful in the hilly terrain. Even with a lot of the time spent in 2nd and 3rd gears and sustaining 3000 to 4000 rpm** over some stretches of curves, there were times when I was dropping into 1st (remember altitude plays a role too). A little more "dig" would have been welcome; it would have put the LT5 into its sweet spot - above 5000 rpm+ more easily.
**From the perspective of lingering in the 3000-4000 rpm range, it occurred to me that would put an LSx or perhaps even the new LT1 (C7 motor) right in their sweet (torque) spot - assuming at or close to the same rear gear ratio. Those LSx motors' (torque) peaks earlier (at less rpm) compared to the LT5, and in that particular application they would out-pull the LT5s unless the ZR-1 had something like the 4.10 ratio to bring the LT5 rpm into its prime torque vs. rpm range too.
That said, the results from last year's running of the 1/2 mile in Monee clearly showed where the LT5s shine. As Pete mentioned, the LT5s are obviously long-legged; pretty much dominating LS motors at that event in spite of the LS boys having a cubic inch advantage. (limited to NA motors, that is). I would attribute that to the fact that venue favors motors with peak hp in the high rpm range. The 3.45 geared Zs did very well for themselves! But, there were reports from the 4.10 geared LT5 guys that in that venue the cars would nose over when hitting 5th gear (somewhere above 120 mph).
So, the 4.10s in any one gear will increase torque at the wheels, and thus acceleration - in that gear, taken on the whole in a distance/speed venue vs. a hilly/twisty course (with altitude tossed in) ether the 3.45 or the 4.10s have their special place.
For now, I will admit the 4.10s are fun, especially on the street. But, taken on the whole - the extra shift in the 1/4 mile mitigates most of the advantage of the 4.10 gear for the ZR-1; at least for that venue (maybe if one power shifts, the extra shift could maybe be overcome to result in favor of the 4.10s...
but not with MY ZF transmission - thank you very much!!). AND, hitting the 1/2 mile at the top of 4th with the 3.45 - is about as ideal as you can get for that application.
The 3.45s are evidently pretty good "all round" for speed/distance up to 1/2 mile contests (sans possibly power shifting). However, for mountain thrills...the 4.10s would have been VERY nice to have. It boils down to the venue, I recon. Too bad we don't have quick-change rear differentials like we had in modified stock (dirt track) racing. In under 20 minutes you could change the ratio to fit the speed/rpm equation for that track.
I'm thinking I'd love the 4.10s for street and cruising the twisties. But, for speed/distance contests, the 3.45s - up to 1/2 mile - it's pretty hard to beat the versatility. Even if one goes with a compromise between 3.45 and 4.10 (or 4.30s?) that gear too would favor certain venues at the expense of some other. Decisions, decisions....
Maybe the answer is to have multiple Zs, each with different ratios and simply choose the Z that fits the situation. Yeah... I LIKE that idea!