| I suggest that you keep the 525 chain size. The high torque and weight of a 999 requires it. More torque means more chain tension and a 520 chain has a ten percent lower tensile strength than a 525.
SP, SPS, R and Corsa models have even higher torque outputs you say. So how do they survive with light-weight 520 chains? That’s easy. Once you get over a certain torque level (for a given weight bike) the bike will wheelie before the chain tension exceeds it’s strength limits. At least for awhile ... chains on these bikes don’t usually see 15,000 miles of service.
Bike weight is the key. The heavier the bike, the higher the chain tension needed to make it wheelie and the higher the maximum chain tension it will experience. So, a 680 pound 9XX-plus-rider will generate a higher chain tension than (say) a lightweight Corsa-plus-jockey or even a Suzuki GS-X. Reports of chain failures are common enough, so it may not be wise to ignore this point for the sake of saving 275 grams of chain weight.
DID supplies chains to a number of manufacturers. So, for appearance sake, if you that want a D.I.D. gold link chain without having to switch to a 520ERV or VM set-up, you can order Honda part number 06405-MAS-003 for a 96-97 900RR which is a is a DID 525HV but with gold side plates.  | 
Shazaam!
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