When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
If you want the most aesthetically noticeable mod, do one of the front lips first.
If you want the most audibly noticeable mod, do the exhaust.
If you want improved handling, eibachs.
I installed my Tanabe before my Eibachs, and I was a lot more excited to be able to take turns quickly and comfortably than to hear the nice deep tone of the new exhaust. So personally if I had to choose, I'd lower the car first. That improves your driving experience the most IMO.
Here's what I'd do if I was tight on money. Get the Carlsson lip first, then the Tanabe exhaust and slowly save for the Eibach/rims last. You will gradually improve the look of your IS w/o breaking the bank. My top 3 would be lip, rims/suspension, then sounds. Then some F-sport goodies, Wald rear spoiler, and TOMs side skirts. Mostly going for aestetics than performance.
i like the carlsson if you are only going to do a front lip, if u are planning on the whole kit than the fabulous is nice also. I like the OEM front lip the best thou