I received my XSi back from MaxMax (LDP) today after they converted it to full spectrum for me. In addition to the conversion I also got two IR filters, one with a 50% cutoff at 1000nm (left) and the other with a cutoff at 715nm (right). In the image above, I have processed both to maximize contrast. The differences aren't that obvious but the 1000nm one has high contrast in the sky while the 715nm has more balanced contrast and detail in the trees. If you view these images in RGB, the difference is more pronounced.
The 1000nm image has data more even spread across the 3 RGB channels, where as the 715 cutoff image has much more data in the red channel. In order the get a suitable exposure the 1000nm cutoff image required 4-stops of additional exposure time as opposed to the other image. I think both will have their distinct uses, the 1000nm cutoff will be great for landscapes with dramatic skies where as the 715nm cutoff will be more suitable for images with strong foliage.
MaxMax (LDP) also makes IR filters with other cutoff frequencies along with UV-pass filters. Someday I'll get around to exploring those, but I have my hands full for now.
Technical Specs: Canon XSi (full spectrum), 24-105 @ 24mm, f/4, ISO 200.