Apologize for getting back to you so late on this.
If I look at database performance as measured by TPC*-C (I don’t have Oracle data but do have IBM DB2), we saw about 1.56x scaling from Dual-Core Xeon 7140 (4 processors) with a result of 331k online transactions per minute to Quad-Core Xeon 7350 (4 Processors) with 516k online transactions per minute. We also did some internal OLTP measurements comparing 2S Quad-Core Xeon 7350 vs. 4S Quad-Core Xeon 7350, estimating about 1.85x-1.95x scaling as you move from only 2 processors to 4 processors, depending on the workload. Lastly, we estimated about 20% better scaling on the E7350 vs. the E7330.
So, what does all this data mean? Well, if we focus on your 8-core constraint (I’m assuming this is due to processor license agreement you have vs. a site license or EULA with Oracle), and if transaction performance was your #1 goal you would be best served with the Four Dual Core 7140 processors. This conclusion is based on the fact that E7140’s best TPCC score was 331k transactions, that the 4S X7350 scaling over 2S was ~1.85x better (516k / 1.85x = ~280k transactions), which is about 20% less estimated transactions than the E7140s.
However if transaction performance is not your only goal and you want to achieve more energy efficient performance and want the performance headroom to grow into more processors, you’d be better off investing in the Quad-Core Xeon X7350s (8M Cache, 2.93GHz, benefits of the energy efficiency benefits of the Intel Core™ Microarchitecture, socket upgradeable to the newest Intel 7400 based platforms, etc.)
I also would like to suggest that you consider a third option, and that being two new Intel Xeon E7440 (16M Cache, 45nm hi-k, better energy efficiencies). These are the newest quad-core processors (we also have 6-core options at the top of our processor line up) and would enable you to stay within your 8-core constraint, while giving you even more performance headroom in the future if you upgraded to 4 processors. Lastly OEM Systems equipped with the Xeon E7440 processor should be less expensive than OEM Systems equipped with the Xeon E7350 processors.
Hope this is helpful.