Mail and web enterprise protection recommendations required

Looking for email and web protection solutions,
Im taking quotes at the moment and have dismissed Barracuda simply because their mail rules are only able to be setup in 1 direction not both at the same time. Ive dismissed MailMarshal and webmarshal or Marshal as they call themselves these days as they never return your calls.

I already have quotes from
Messagelabs
IronPort (now part of cisco)
But looking for other well proven recommendations

We have a rapidly growing company 150 users spread across 6 UK sites at the moment but soon to expand this year to 300 users and buy up 2 more smaller companies with 2 extra sites.
Messagelabs is appealing because I know there system inside out having used it at my previous company last year and its easily scalable and is very good with a guarantee that nothing gets through, mind that has a downside if set too vigorously it could capture false positives but you can easily set up a quarentine mailbox to check these, however it is expensive.
Ironport is highly recommended by numerous contacts in the business and is now owned by cisco.

We at the moment have one 2003 SP2 exchange server at HQ which obviously feeds all the other sites.
The rest of the servers and clients are 2003 and xp all service fully packed.
We are looking for a package preferably not software but either hardware or managed service similar to messagelabs which scans all email for spam and AV along with a proxy for scanning for viruses/spyware etc.
Using this we would then be really well protected from mail and web infection obviously no system is 100% but I want something that gives the best protection available with a lot of flexibility with regards to rules and scalability, the clients have av running from our central av server.

Please only sensible recommendations please.

Thanks for your time.