Thank you coffeecat!
I tried using the deep scan with testdisk, but all it found were impossible large partitions at the end, so no truecrypt partition
I used fixparts with success, but all it did was wrapping the extended partition around my /sda5, so I started playing around with sfdisk myself:
I noticed that when using "sfdisk -f < parts.txt" to use the backup, it already warns about the too large partition size and even gives the maximum possible size, so I edited the parts.txt directly, adjusting for the highest possible size and it set the extended partition as it should be!
This worked fair enough, so I added the sda6 manually using
# partition table of /dev/sda
/dev/sda1 : start= 63, size=715133408, Id=83, bootable
/dev/sda2 : start=715134976, size= 204800, Id= 7
/dev/sda3 : start=715339776, size=209504256, Id= 7
/dev/sda4 : start=924844095, size= 51929073, Id= f
/dev/sda5 : start=924845985, size= 8385912, Id=82
unfortunately this didn't work for truecrypt... guess I will have to go to the truecrypt forum now.
/dev/sda6 : start=933231897, size= 43541271, Id= 0