Looking for some advice.

We want to setup a dedicated chatblazer server and are reviewing several softlayer configurations.

At the lower-end we're considering either the AMD 170 or AMD 185. AMD 170 is 2.0Ghz dual core, while the 185 is 2.66Ghz dual core. The difference is the $99 setup fee payable on the AMD 185. Would there be enough performance benefits going with the AMD 185 over the free setup 170?

The other option we're considering is the AMD Opteron 270 4 x 2.0GHz. Which has double the RAM (2gb), dual processor and costs about $100 a month more.

We're looking to host around 1,000 concurrent chat users initially, but expect to see those numbers grow rapidly in the months ahead. Our thinking is start with one of the cheaper servers to benchmark some numbers and then look to possibly upgrade later.

Any advice?