eerrmm. no.
if they changed direction quicker then in theory they will open the valve earlier. if the valve opens earlier then the engine will start mis-timing and you lose power.
the cycle of the tappet is very simple - down and then up - you don't want this to happen any faster or slower otherwise your valves will open and close at the wrong time.
but that won't happen anyway.
the next issue is that tappets do not have any performance qualities what so ever. They are merely a device to keep a pressure on the valve and to open and close it at a predetermined time.
from my quick look at part numbers - all VWs up to 95 seem to use the same tappet. there is no "performance" tappet. A tappet is a tappet is a tappet.
in theory you can change a single tappet. if that tappet performed any differently than the rest of the tappets then you would have serious problems on your hands. you would certainly get some form of valve overlap.
however, it transpires that all tappets are the same, they open the valve, they close the valve.
what is interesting is that some company has told you that they make a difference - when the part is the same!
i personally would still use the original VW part.
