Treating your old KH29 to an upgrade as per Nurse Ben’s advice are we 
I have been riding mine from when they were first released and it was my first wheel build.
I have had no problems at all the disc side spokes do have a fair bit of tension compared to the non disc side to keep it dished correctly but the build was straightforward and as I stressed relieved it as I built it I have never had any issues with it going out of true and that is with 2mm / 1.5mm / 2mm DT Revolution DB spokes.
I will rebuilding it into a KH29 frame next week (with the awesome Hans Dampf) which is a shame as it has been such a top wheel but I am hankering for that bigger wheel buzz 
I will post up a build thread when I start which might be of interest.
When you think about it whilst we may have more torsional forces on our wheel (which the tyre is probably taking the brunt of) bikes have massively dished rear wheels with their 9-10 speed free-hubs (far more than the Oracle hub) and they don’t have any problems and if you think how many of those have our are being used over decades I think it safe to say a dished wheel built well (or not that well with my amateur job :p) will be absolutely fine. Bikes also are a lot faster so hit things far harder and the big DH/freeride boys are doing massive drops and jumps on them.
I think the only rare issue is creaking (which i have not had) which is an issue with all multi piece/material KH hubs as the flanges sometimes move on the axle.
On top of all that I think they look so much better than the crank mounted disc brakes IMHO
I am sure Nurse Ben will put his thoughts in to the mix soon being more of a kit whore than me and owning about 47 wheels with them in 
As for spoke length Roger at UDC uses a 287mm for both sides with long 16mm nips (so 288mm with 14mm nipples) on a KH freeride rim 606.5 erd, with your XC rim with a 608mm erd you would need an extra 1mm on those lengths, obviously check for yourself my recent spoke exploits (due to nipple length variations) makes me not trust anything anymore
Hope my ramblings helped