i used to use barsto barrels exclusively since its very accurate and is the standard for barrels.
When i bought my svi it had a scheuman barrel installed, i thought what the heck and shot it as it is. surprise surprise same accuracy. 8,9 ring of a rifle target at 50 meters.
as for the difference in sps and sti, i think the sps cannot be sold in the usa since it had copied the stisvi product. dont know about the quality or durability though. further, they are pricing it the same as sti svi in the philippines. its a no brainer on which to buy. tried and tested or you get my point