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If they both work well, I'm now thinking I'd recommend sticking with the r213 mod. It has the least modified files, as well as the r213 separate process stuff which should allow it to process larger images.

On Win7 x64 with CS6 x86, it seems to be able to handle up to the following dimensions for freshly opened images:

B5 8-bit @ 13308x18784 (1856 ppi)
B5 16-bit @ 10074x14220 (1405 ppi)

A4 8-bit @ 13312x18766 (1604 ppi)
A4 16-bit @ 10110x14250 (1218 ppi)

8-bit @ 16384x16384
16-bit @ 11648x11648

That it can just barely handle A4 16-bit (48-bit color) scans @1200 ppi is the only interesting limit out of the above, considering 1200 ppi is the optical resolution of many scanners.

You probably need at least 6GB of RAM to reach these limits though.
(Photoshop 3GB + Greyc Helper 1.4GB + Windows OS 1GB)