Yohimbe has a tricky dose/response curve relative to other nutraceuticals. Having said that, here is my input:
3-5mg of Yohimbine HCL OR;
1-2ml of MASS Yohimbe Supreme
Yohimbe's real value here is in prolonging/intensifying noradrenaline re-uptake released by the caffeine/1,3, ephedrine etc. Yohimine HCL does this the cheapest, but for my money still feels "dirty".
The Yohimbe Supreme product is the only full spectrum Yohimbe I've used that doesn't feel dirty and is consistent enough from batch to batch to reliably use. Yohimbe extract for example, from Beyond a Century is incredibly volatile from batch to batch and even dose to dose IMO. I go into much greater detail in The Blueprint (google Organic Anabolism to find it) but suffice it to say, Yohime Supreme is a smooth ride.
Again, Yohimbine HCL is a fine product and likely your best bet from a price point perspective. Too much vs. just enough though, leaves you jittery, paranoid and with skin crawls.
Hope this helps..