ICE does not appear to have a general 5K panorama-width limit. In normal use, you should be able to set the output scale to 100% before export and get the maximum available resolution.

Based on the reports here, the restriction is likely tied to your source or export format rather than panorama size itself. Several users found that ICE limited output when working from RAW/DNG files, but allowed full-resolution output when those files were first converted to TIFF (or when using JPEGs).

So the practical workaround is:

• stitch at 100% output scale in ICE
• if DNG files are limiting size, export them from Lightroom or another RAW converter as TIFF first
• then stitch/export from those TIFFs instead

There may also be a very high overall image-size limit in ICE (one answer mentions about 537 megapixels), but that is far above 5120 px wide in most cases. In short: this is probably a DNG/format handling issue in ICE, not a normal panorama-resolution cap.