That is basically it... but if your queries are returning all of the records then you are getting little out of them, and will only get minimal gain from switching to SQL Server.

It would be better (no matter what database, but particularly a server-based one) to also restrict the amount of rows that are being returned.

How you should limit the rows depends on your data and application. As a simple example, in an insurance system you are likely to want data for a specific person, so you would allow the user to type in the persons name, and then use that in the query, eg:
Code:
SELECT FirstName, Surname, ...
FROM tablename
WHERE Surname Like '*Smith*'
ORDER By Surname
With your wireless network this kind of thing is likely to make a massive difference to the speed, particularly if you switch to SQL Server.