Performance gain by moving a large table from a database and referencing with a synonym We have SQL Server 2008 R2 database which is currently about 80Gb.

About 10Gb of this is down to one table, and I wondered if there would be a performance gain if I moved this table into it's own database, and created a referencing synonym so that existing queries and SPs remained functional.

This database is ripe for an overhaul anyway, so that may be the obvious answer but I wondered if the synonym idea would be a quick win.
You don't have to move it to it's own database. You may be able to get a performance improvement by simply moving it to it's own filegroup within the existing database.  The filegroup could then contain one or more files that are on a separate disk(s) from the ones the rest of the database is on.