If the conditions in game match real life, you will get comparable lap times in a good simulation. Rene Rast was running within a second at LeMans for example, using Project Cars. It's not hard in AC to do the same thing if you set the track grip levels at less than optimum and with comparable ambient temperatures but many times, even under optimum conditions, times are very, very close. Wikipedia, for example, lists the best GT3 lap time at Brands Hatch as 1:23.268 in the Audi R8 LMS Ultra. In Assetto Corsa it's 1:23.398 and in Project Cars it's 1:22.720. Emerson Fittipaldi qualified the Lotus 72D in the 1972 British Grand Prix in second at 1:22.600. Fastest time in AC on RSR is 1:22.438. Note also that most times on the leaderboards are considerably behind that and only the uber aliens can get close to those best lap times. Of course in a sim you don't have to pay for damage or worry about injury or death so you can go 10/10ths all the time and lap times will probably always be a little faster in matching conditions on the sim. But close lap times, I expect that.