My 2 cents. If you simply want a super quick car then by all means dish out another 25k and get the GT-R as there is simply no way to shoot its numbers down, it is SICK FAST! It is also LOUD so you will be talking over the noisy interior to get your passenger to hear you. The IS-F is a 4 door performance sedan and is purpose built as the GT-R is. You are still able to take the wife and kids out on an excursion, as well as add a abay seat if needed. Its an all around performance sedan with supercar numbers but NO it will not get near the performance of the GT-R but it will do a lot of things the GT-R can not. Its just a personal preference of needs at this point since they are both two totally different purpose built vehicles.
Andy
Andy