IMHO, both the bonito and the xzb speed are both great engines. Like Niel Said it depends on your tuning skills. I can never fine tune a nova. I can see nova guys here tune thier engine during the morning and tune it again in the afternoon when it gets colder. The XZB speed, I tune it in the morning and if it runs great, I let it be. It holds it tune in the afternoon even if it gets colder. I am not a good tuner but for some reason I know when an os engine is tuned right just by the sound of it.
I think the bonito brings more power than the speed. Usable for a truggy but can be a handful in a buggy. I run the speed in my buggy. However OS engines looses it pinch easily but it doesnt mean that it wont run good anymore, it just the way they are.
I like an engine which is forgiving in tuning so I like the speed. Also as suggested check out the JQ the Car Engines. It was based on the older speed which to me is much more suited for buggy. The XZB speed is just a monster with a 2058 pipe or a 2090.