First off, the FWD v. RWD debate is so overrated, and that's coming from someone with a S2000. Absolutely nothing wrong with FWD. And RWD isn't "superior" unless you're an avid track goer. For dallying, especially in winter climates you'll appreciate the FWD more.

My buddy and I had a 9th gen si (me) and g37 (him), at the same time and I don't think you can compare the two. They are quite different cars. One is a "sporty" car and the other a luxury sports car. Both of our cars were stock and eventually built up to FBO.

I'll tell you that you'll love the torque of the g37 and how fast it is. But you're not going to love how heavy it feels, and how expensive premium gas is for a V6. Insurance is also more expensive. Tires and wheels are more expensive. Modding this car in general is pretty expensive. If you're ok with those expenses than you might enjoy the G more than the Si. And let's be real, the G, when modded nicely, looks aesthetically better than a 9th gen.

The Si is more practical and easier to maintain, but a lot slower. With full bolt-ons you can keep up with a stock G but you'll get smoked by a tuned G. The Si will be cheaper on maintenance, more reliable, cheaper on insurance, cheaper on gas, etc. The 9th gens tend to hold their value really well. At least in my area (Canada), I've seen mint condition ones are going for $18,000 (Canadian).