When Ramshot introduced Silhouette their first ballistician said it was exactly the same as WAP. Ramshot even used the former Winchester WAP data for quite some time until they generated their own data later by Johan Loubser whom Western Powder Co. acquired when they bought Accurate Powder Co.
IMO, there's not a better powder for defense loads in 9mm and probably .40 S&W but I only use 124 gr. JHPs in 9mm. Ramshot lists some nice .38 Sp. +P loads and there are probably better powders for standard pressure .38 Sp. Target loads. In .45 ACP, I use 7.5 grs. of Silhouette with the 230 gr. ZERO JHP that is very accurate at 839 FPS from my 4.5" SR45. I'll be testing 7.6 grs. next time out to see if it gets over 850 FPS without overdriving the bullet which I've done at 7.8 grs. that averaged 917 FPS for 10 shots. The ZERO has a good core, but at 917 FPS it loses its jacket in my water jug tests.
With the 185 gr. Golden Saber, the current Ramshot ballistician disagrees with the former ballistician, Johan Loubser, as well as what I've observed. He claims higher velocity with less powder where that's never been the case, IME. I believe he has gone to testing with minimum dimension barrels for his pressure tests and when I asked about that, I never got a reply. For a 185 gr. XTP, Ramshot lists 9.9 grs. of Silhouette as the Max. Charge for 1152 FPS. Going back to older Accurate data provided to me by Johan Loubser, at the same charges, the 185 and 230 gr. Golden Sabers ran at least 50 FPS slower than the same weight XTP's with pressure lower by as much as 2000 PSI. For my own defense load, I worked up to 9.9 grs. of Silhouette with the 185 gr. Golden Saber. It chronographs 1087 FPS from my SR45 reconfirming Johan Loubsers data for AA#5 and #7 up to +P loads. The 9.9 gr. charge with the 185 gr. XTP @ 1152 FPS was tested to be below the 21,000 PSI limit for standard pressure .45 ACP. My 185 gr. Golden Saber load will penetrate deeper than a conventional 230 gr. JHP while expanding to over .750".
When I shot .40 S&W I made a lot of loads with Silhouette including cast lead. The only powder that I've found to be any more accurate is True Blue. I never really compared muzzle flash and WAP/Silhouette is excellent in that regard as it's treated to give very low flash. True Blue kinda comes by it naturally from being so fine grained and dense, IMO. For that reason I favor Silhouette for defense loads even in .45 ACP and few powders have more performance potential at the same pressure level.