We are going .net for the next version, investigating other database engines, but I am sure we will stay with Advantage Database Server.
I'm going to get a C.NET course though 
I don't want to know Visual bloody Basic - it's crap!
vb.net, esp 2005 and 2008 versions is much better than the old ones. language is irrelevent in .net. My own view is c# and vb.net are the most productive, c++ is a bit clunky in .net.
if you're going .net, ms-sql will become the natural db choice, due to excellent integration, and the freebie version is good enough for most things (replication aside)
I cannot stand VB6 the IDE is rubbish and I can't stand the way it breaks my careful formatting.
I want = to line up in a column and they will 
As to ms-sql - we will have to benchmark against our current server, which started as a reindeing NLM about 15 years ago and became a server in its own right about 12 years ago (V3) and is now one of the best performing client server engines (V9) - which is also platform neutral NT, NW & Pingu.
I would like to try Vulcan which is VO.NET
remember vb6 is about 10,000,000 years old. However, if you need columns in vb6, ole in excel if you can guarantee installed, or use MS Flexgrid included with vb. Even in .net, still use a grid control

MS-SQL and Oracle are the 2 fastest in the mid range server market. Which of these is fastest depends on the query and whether 32 bit or 64 bit. MS SQL is Windows only, Oracle is more for Unix, though Windows versions available. MYSQL is making inroads now they have improved scalability.