F31fd vs 40fd for someone with SD cards

I'm looking at the F31fd, but saw the 40fd now uses SD cards. I have a Canon S3 which will be used mostly for outdoor shots and the Fuji for indoors and light travel. I really like the idea of not having to have separate cards for the Fuji and it will save $40 or so buy not having to buy a couple. What are big differences between the 2 and will I loose much low light ability with the F40 shooting at 4-6MP and printing no larger than 8x10?