I of course would recommend a PRIMEPOWER over a Sun box! ...as we have the following;
7 pipelines
2080 entry instruction TLB
High-throughput internal buses (multiple times faster than Sun's)
Sys Interface at 4.16GB/Sec (compared with only 2.4GB/S with Sun's US IV+)
Out of order execution
non-blocking cache
etc. etc.
Our single core SPARC64 2.16Ghz/4MB is way faster than their fastest dual core USIV+. We are releasing our dual cores later this year and Sun are partnering with us so we will both be using the same technology (still designed by us though).