Recently activated a smallest windows rackspace cloud server (512M RAM, 20GB disk, win2003 server 64bit).
Performance is a lot better than expected. After login the server has still over 250M RAM free.
It's a 4x Quad-Core AMD Opteron(tm) Processor 2374 HE (2.2GHz, 7GHz IMC, 512kB L2, 6MB L3). CPU slices are capped, but still.
SiSoftware Sandra

Benchmark Results
Aggregate Arithmetic Performance : 26.28GOPS
Dhrystone ALU : 28.87GIPS
Whetstone iSSE3 : 23.7GFLOPS
Benchmark Results
Aggregate Memory Performance : 9.33GB/s
Integer Buff'd iSSE2 Memory Bandwidth : 9.25GB/s
Float Buff'd iSSE2 Memory Bandwidth : 9.4GB/s


They also have some serious disk subsystem: