JusticeT - In line with DaleS post above and yours, pressure is what you make it - in any case when handloading. You can make it higher, or lower - you have control and are ultimately in the right, or at fault, depending on the outcome.

Smokeless powder in longer cases can develope lower pressures at the same and even slightly higher speeds than a shorter case can - but, the longer the case, the more critical the powder choice becomes and the greater the need for fillers when lighter than full case loads are used to keep pressures down. Fillers are not to be feared, but must be understood & used correctly. Many here use them succesfully.

We see in the manuals, that the longer cases in .458 can exceed the .45/70's speed when loaded to the same pressure, but the difference is not great within the lower pressure ranges. To increase speeds substancially the lower pressure ranges must be exceeded. In the lower ranges, the difference is minimal and actually reverses with some powders. Powder choice is critical. It can take a LOT more powder just to match the shorter case's speed and pressure just because the shorter case can use a powder that the longer case cannot. This is one reason I said powder choice can become critical.

I have a friend who loads his Marlin to 1,795fps with a 405gr. bullet and loves that load for moose and elk. His load developes 28,000psi according to the mannual. My Sharps gets 1,785fps with the same 405gr. bullet and my load is listed at under 22,000psi/cup. I used a different powder because I bought a manual he didn't think would help him - afterall, he aleady had a manual.

As easily observed by anyone in Hodgdon's Annual Manual, a 24" bl'd. .45/70 can be loaded to around 1,800fps with 400gr. bullets and pressures kept below 28,000psi. It can be loaded also to 2,000fps and still, pressures are at 40,000 or less with a couple powders, however to exceed that speed by enough to make it useful, pressures must be increased considerably to 50,000psiand more. IIRC, the longer, 3 1/4" cases produced higher speeds at a reduction of around 5,000psi from the 2 1/10" case. The in-between cases, produced in-between ballistics. There was not a lot of difference between long and short, straight cases. The volume %age does not change quickly.

This can also be seen in comparing the 2.5" .458 WM and the .458 Lott in the same manual. I used the Barnes manual and the Lott shows a tich over 100fps advantage with the 500gr. TSX, solid and 600gr. RN - yet it's case is considerably (.300") longer than the short mag's case.

It's velocity is not much higher & virtually identical for most of the loads listed, ie: 50/60fps difference - about the same (or less) you get from one rifle to another. In animal terms, not enough to make a real difference if identical bullets are used.

Don't read me wrong, this is not an argument in comparing these fine ctgs, but merely to show that in straight cases, it takes more than a little bit of length to make a big 'enough' difference to be 'felt' at the receiving end.