I was in a similar situation before I decided to go into the company car scheme - my budget for a self-purchase would have afforded me a 3 year old IS-F, which was so so tempting, but in the end, I had to look beyond the noise, and speed, and think logically. Having driven the IS-F a couple of times I can say that it is an absolutely blinding car - the noise is intoxicating, but... and it's a big but... (I'm sure the F owners will confirm) running costs are huge: Tyres, road tax, fuel, servicing, pads, etc, etc - and if it's over 3 years old, you'll be out of manufacturers warranty. Although granted, probably not required... but it's always peace of mind.
Probably best to sit down, work out your budget, then take both for a drive. They'll be chalk and cheese of course.