24-105mm vs 24-70mm Distortion!

Here's a refreshing change. A request for advice between the 24-70L and 24-105L. But I'm not interested in sharpness.

I currently use a 5D with 24-105mm. Its great for travel etc and walking. Both lenses mentioned are sharp so thats not an issue.

But what I find hard to deal with is the distortion of the 24-105. I'm well aware that my CS2 software has a remove distortion feature. However, it never seems to remove the bowing horizons.

I'm not sure of the different geometric terms for different distortion. However both the CS2 software and (a trial I had of) DxO optics pro leave me underwhelmed.

I like to shoot panoramics, and sometimes at 35mm they knit together OK but leave a silly shaped horizon.

So my questions are:-

1. If I upgrade to 24-70L would it markedly help my panoramics? (Its not always possible to shoot beyond 50mm!)

2. Is there any way using photoshop to improve horizons other than 'lens correction' tool.

Thanks in advance
Rob