hice mis pruebas de a 1000 en 1000
y con 8000
es lo maximo en caracteres que soporta.
Código SQL
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GRANDECADENA VARCHAR(8000) CHARACTER SET UTF8 COLLATE UTF8,
GRANDECADENA VARCHAR(8000) CHARACTER SET UTF8 COLLATE UTF8
como lo dice aqui
http://www.firebirdsql.org/manual/mi...ata-types.html
Variable-length non-Unicode data with a maximum of
8,000 characters. Firebird can hold up to 32,765 characters. In 6.5, maximum was 255.