I'm gonna hurry up and get in here before the haters start posting saying "Don't buy a console for one game!" Well guess what guys? I bought a PS3 for God of War 3 and I'm glad I did so if you want to buy a 360 for Black Ops I say do it.
First of all I'll pretty much guarantee there will be a Black Ops bundle. MS signed a 2 year exlusive DLC package with Activision for COD and MW2 had a special console bundle. I'm pretty sure Black Ops will have one as well. Most likely it will be the 250GB with 2 controllers and Black Ops for $399. Now as you said you don't necessarily need the extra controller so if I was you I would just purchase the 250GB and buy Black Ops when it releases. You will save $40 by not purchasing the bundle. I recommend the 250GB (I have one myself) because I prefer installing games therefore not having the discs spinning the whole time I'm playing games. Its completely silent with games installed with no risk of disc reading errors or it becoming worn out. Also the built in WiFi is clutch (I"m assuming this is why you are buying a router).
The reason I suggest definitely buying the 360 for Black Ops is because you aren't necessarily buying it just for Black Ops. Once you get the 360 you will realize the 360 has an amazing portfolio of games. Gears of War for example is an experience that can't be missed. The Fable series is another that is great. You mentioned Halo:Reach and trust me its one of the best FPSs I've ever played. I already have over 30 hrs logged in on that game in just 2 1/2 weeks. FPSs just play different on the 360, and by different I mean better. When you get the controller in your hand and get used to it you will see what I mean.
I bought a PS3 a little over a month ago because I wanted to play God of War 3 and it opened me up to more games like Uncharted 2. Now I have certain genres I buy for the PS3 and I'm glad I have the best of both worlds. When you get your 360 you will be glad you have both because the 360 is better for certain games, while the PS3 is better for others. FPSs is where the 360 dominates and I urge you to definitely pick up the 250GB slim.
