You and I are in the same boat. I lost my IS300 back in 2011 to total loss in an hit and run accident. I have had 5 various cars since then, including late model Mercedes and even some brand new cars. Nothing was as great as that car was in my opinion. The IS will always hold a special place in my heart!
I am too looking for an ISF. Fortunately for me I am in the car business, being a partner in for a small boutique high end exotic car dealer I've had several M3's, over the years in my inventory. They are great cars, but I am a much bigger fan of the F. Maybe I am partial to Lexus, but to be brutally honest... BMW's are a hunk of shit. Of course this is subjective, however the M3's seems more cramped, less comfortable ride, cheaper interior and an annoying noises that those cars make from the interior. For god sake it has its own damn ringtone if you don't put your seat belt on, or have a tire half a lb low of air.
I am personally a fan of the quality of the interior of the ISF, as well as the navigation and touch screen over BMW's I Drive. I also believe the F is a more fun car to drive, sounds better and has more low end power.
Those are my 2 cents from a guy who has been around many of them since the M3 and ISF came out in 2008.
From what I am looking at in my search, the '08's had a few minor issues such as water pumps, loose rear view mirrors (Think this is a Toyota issue, my BRZ had them problem with under 2,000 miles and it fell off twice) and I've heard of some issues of the cars pulling to the right I believe. Not sure if these were completely worked out for the 2009 model, but this is the year I am searching for. Anything newer is too much for me personally right now, as I am recovering from losing my Cayman and Z06 in a divorce.
My search consist of a low mileage '09. In Ultrasonic Blue
I have access to Lexus service history, on any Lexus that has been serviced by a Lexus dealer. If you find a car that looks like it may be a good fit for you, shoot me the vin and I'll gladly email you the service history on it.
Good luck on your search! Go for an ISF!!!