my oldman has A14 Supercharged and it gets cleaned up by the CA and SR datsuns. the Aseries is quick for a 1.4lt engine, but then the CA's and SR's are extremely quick for a 1.8 and 2.0lt - plus they have the advantage of twin cam, injection ect.
the forced Aseries is great if you dont want to mod the tunnel (bigger box), cut up your front for intercooler ect.
value-for-money the CA is the go, more expensive anitially but think about it - you start off standard with 130 - 160kw without touching the engine! the fuel injected CA would be a better driving engine too cause the superchargeD A14 engine is tricky to drive!
but then again the changing of diff, crossmembers, hydraulic clutch all gets too expensive. but the Aseries will still get nailed by the SR or CA cause yes my brothers SR Smokes the Oldmans A14S - im sticking too my standard A14 easiest way to go.