someone kindly flamed me offline rather than publicly (nice) that race sag is actually the diff between the length from axle to mudguard with the bike ON the stand and from axle to mudguard off the stand with rider onboard.
the mxa etc test riders go on about how good a 3mm sag change is (or 3mm drop in fork height or fork oil height or dropping one tooth off rear sprocket or next leaner/richer jet) but for 'us', we'd never notice the difference. just get in around 100mm and forget it. and - hot tip - another useful set-and-forget is take back shock off and make some sort of a mark on the bike to mark how much chain slack is needed at its longest point to ensure pressure not put on countershaft bearing (when there's no slack). i don't know how often i turn up at a starting line to see guys' chains at full stretch when seated on the bike.