Given only speedups any formula to combine them is meaningless, because the real question involves a concrete workload: would the performance of what I'm going

Given only speedups any formula to combine them is meaningless, because the real question involves a concrete workload: would the performance of what I'm going to do with my computer improve enough to justify the cost of improving it? At the very least, weights for each benchmark task are needed; complications of the cost model (beyond a binary old system/new system comparison) are also likely. Measuring performance improvement by speedup of throughput is also often naive, since there are other dimensions (like power and latency) and complex requirements.