>Maybe I should use LatitudePlusDistance/LongitudePlusDistance from http://blogs.lessthandot.com/index.php/DataMgmt/DataDesign/sql-server-zipcode-latitude-longitude-pr

Try this simplified version and see if you could get something better:

DECLARE @CenterLat Float=47.7795
DECLARE @CenterLon Float=-65.7191
DECLARE @SearchDistance Float=250

SELECT Result.Latitude,Result.Longitude
 FROM (SELECT * FROM Test T
 CROSS APPLY (SELECT SIN(@CenterLat/57.2957795130823)*SIN(Latitude/57.2957795130823)+
 COS(@CenterLat/57.2957795130823)*COS(Latitude/57.2957795130823)*
 COS(Longitude/57.2957795130823-@CenterLon/57.2957795130823) AS Temp) Temp
 WHERE (Latitude>=@CenterLat-@SearchDistance/111.0 AND Latitude<=@CenterLat+@SearchDistance/111.0) AND
 (Longitude>=@CenterLon-@SearchDistance/111.0 AND Longitude<=@CenterLon+@SearchDistance/111.0)) Result
 WHERE 3958.75586574*ACOS(CASE WHEN Temp > 1 THEN 1 WHEN Temp < -1 THEN -1 ELSE Temp END)<=@SearchDistance