0-60 times I believe are 9.9 secs for the 1.8 litre (fabric top & Roadster Coupe) & 7.6 secs for the 2.0 litre fabric top, 7.9 seconds for the 2.0 litre Roadster Coupe.
Both cars are nice but the 2.0 litre’s the one for me - would recommend not just for the improved 0-60 time but as other folk have said it’s a more flexible engine due to increased torque, also 2.0 litres in Sportech trim come with the other sports items i.e. 6 speed box, Bilstein dampers etc. All 2.0 litres whether in SE or Sportech trim come with a limited slip diff, according to my brochure from late 2011. Mazda dropped the 2.0 SE in early 2012.
The 1.8’s a bit easier on petrol although my 2.0 litre regularly manages just over 43 MPG on a decent run.