>Any idea on any speed difference between VFP6 and VFP9 on handling a table of 500,000 records with 50 fields - would SQL be faster or slower than VFP?

I haven't used (or seen) VFP 6 in many years. I have not tested it side-by-side ion the same box to be able to tell you. On a properly Rushmore-optimized table, both should be fast for a sensible query.

Compared to SQL-Sever? (SQL is a language: stands for "Structured Query Language", SQL Server is a commercial database product).
It depends on the test conditions. Are we on the same box? Are we talking about different boxes accross a LAN. Or is it a WAN? Is it Internet? How many concurrent users?. What types of workload on the server? Are the tables and indexes (indices?) properly maintained and optimized?

In some cases VFP will be very fast. In some cases, slow. SQL Server will generally be fast but an improper query or a poorly setup table and set of indices will also slow it down. In short, your question is very broad and has no one answer.