I think that what he is asking is," is a slide carb more or less efficient than your average butterfly valve carb if they came with the same diameter and ratings and stuff like that."
And even THAT cannot be answered as presented
A perfectly dialed in good quality butterfly carb CANNOT be beaten with a same throughput slide carb that's dialed in exactly as well.
A true keihin or a Tillotson butterfly carb outperforms any chinese clone of a mikuni slide carb if you only spend minor time on tweaking them.
(assuming both are nominally same bore)
Sooo without knowing what exactly is to be replaced with what... that question cannot be fully answered.
replacing the crappy carb on a clone industrial with a higher quality carb
gives you more room for adjustability and thus enables you to gain some performance.
if you want noteworthy amounts you need more fuel and the potential to make use of it.
(i.e. higher troughput and ultimately a bigger bore carb)
Again.. not important if butterfly or slide if you do it right, there will be no downside either way
BUT [ and the reason for me not answering the question in the first place]
if you have say a true Honda GX270 with it's true keihin butterfly
you'd be a moron if you replace that with a shingshong slide carb
you might want a true 'next size up' mikuni if you so desire or just the keihin from a GX390 later on instead ;
)
If you have a predator with it's castrated chinese version of a keihin clone
you'll be missing out if you would not at least replace that with a fully adjustable carb
once you modded the engine a bit more than the usual governor removal.
(until then it'll be fine as it is a bigger jet maybe and it's all you'd need to be happy)
There is simply no way to fullfill that request without more information.
'sid