Do large PM boxes affect performance?

[guv]

My site is on a shared server, so accutely aware of associated loading problems.

One thing I have been asked for, is to increase the PM box from the default 50 to at least 200 or higher.

Will this have any affect on performance, or is it just a case of the database increasing in size and no ill affects?

It its not a problem, I'll increase it.

Thanks in advance

[Dismounted]

You database size will increase as message boxes fill up. You should not experience any slowdowns (PM system modifications may affect this).