I most definitely am not.
Brains trust, can I run some numbers by you please.
I've punched my numbers through prowheelbuilder and DT and got similar numbers for required spoke lengths.
Front 290.4 L and 291.9 R - DT recommended 290/292
Rear 291.1 L and 289.9 R - DT recommended 291/290
Would there be an issue if I went with 291 all round to simplify things or should I stick to the recommended lengths?
Will be using SAPIM Race spokes with SAPIM brass 12mm nips and using washers supplied with rims.
Ideally you can run 291 as a single length across the board; easier to keep spare spokes.
The only risk I see is on the front left and rear right you might end up with spokes which are too long (since they stretch a tiny bit as you tension them up. You might then bottom out before you reach correct tension. It's not the end of the world as you can overdrive the nipples which means you lose one or two threads at the bottom of the nipple, and it's of little consequence since most of the load bearing is up the top near the rimbed.
If you want to play it safe, get half 290 and half 291 which should be optimal and give you extra threads to add extra tension later on if the spokes stretch further, or you buckle the rim slightly and need to straigten up the wheel.
EDIT: I assume to get the ERD figure, you actually measured the rims yourself using your preferred spoke and nipple combination? Never use the ERD figure provided by the rim manufacturer.