I actually was almost sold an IS300. At the time I didnt have enough money so I had to wait, and then the coupe came out and all bets were off on the Lexus.
They do not have much power STOCK, however their modding capabilities far exceed the G with out having to change internals. The engine is BASICALLY a naturally aspirated supra motor. There are many boosted cars out there with horsepower in the 400-600 range. Since our cars have such a high compression ratio, our boosting capabilities are limited(STOCK, I know you can change pistons and what have you, but it is limited if you dont change internals).
The handling capabilites are right on par with the G, and I know that caranddriver has better stats for this and that, but believe me, they are very similar in handling. That was one f the factors that almost for the IS.
I personally like the G interior better, but it can go either way, depending on taste. The only thing I despise about the IS are the tail lights.
All in all, I am happy with my G coupe, and I am waiting until an IS pulls up next to me at a stop light[

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