On October 22, Porsche’s latest generation of ‘997’ 911s will be expanded by the addition of two four-wheel driven convertibles – the 911 Carrera 4 and 4S Cabriolets – with up to 355bhp, better traction and better stability than the rear-wheel driven versions.Porsche claims identical performance figures for the more powerful Carrera 4S Cabriolet as its coupé equivalent; both four-wheel drive 355bhp 911s will hit 62mph in 4.8sec and go on to 179mph, it says. In a market where soft-top sports cars are so frequently compromised in the performance stakes, that’s a significant claim. So is it borne out on the road?It certainly feels like it. Despite the additional 140kgs of body reinforcement, four-wheel drive system and folding cloth roof, the lesser 325bhp Carrera 4 wants for no power, and its 355bhp stablemate serves up genuinely urgent and flexible performance. Porsche’s design of the cabrio has been so thorough that they share the same aerodynamic efficiency rating as the coupe, so even on the autobahn, these 911 roadsters are an even match for their roofed equivalents.You have to be determined to expose any flaws over an undulating country route, but with longer springs and that extra weight there is a small loss in outright ability over a coupé. Hit a series of bumps during high speed cornering and the nose bobs around more, requiring extra correction than in a £58k, rear-driven standard Carrera coupe, despite the Carrera 4’s wider rear tyres and wider tracks. The dynamic gap is less pronounced if you opt for Porsche’s Active Stability Management system – standard on the S model - which lowers the ride height by 10mm and keeps tauter control over the 911’s slightly increased waywardness.Albeit the worse-handling ‘997’ to date, it is only when judged by Porsche’s own high standards that the C4 Cabrio falls mildly short. Rest assured that, if you’ve got to have a convertible, neither a Mercedes SL500 nor a Maserati Spyder is as dynamically adept or as enjoyable to drive.