If you're a bit short of inseam, as I am, then longer shocks are NOT better for street riding. I found that the ability to ground both boots at a stop is essential to relaxed riding. The standard 13" shocks carry the standard loaf-of-bread Commando seat 34" above ground. If your inseam is less than 34", you'll approach every stop wondering if you should ground the left or right boot; grounding both is not an option. I was obliged to use 12" shocks, at a cost of an additional 0.75" of rake (slightly less quick side-to-side but a bit more stable on the straight). If this is not your problem, then at least be aware that the rake will decrease with increased shock length, making the bike a bit more nervous in its handling.
Rick in Seattle
1970 BSA 441 Victor Special
1972 Norton 750 Commando Combat
1975 Norton 850 Commando Mk 3