Dedicated Server Host for large forum?

[kyrnel]

<font size="1">I am asking this here because I still cannot access vB.com from home or at work.</font>

I am looking for a good dedicated server for a rather large (but not huge) forum.
Forum specs:
- 20,000 members
- 100-200 concurrent users at peak times
- 500,000 posts
- database is about 600MB (of which 300MB is the search index)

Current Server:
- Virtual Private Server on a dual Xeon with Raid5 (one of 10 accounts)
- 396MB RAM
- 4GB Disk space

When my user count goes above 100, I have no RAM left at all.
CPU load never gets very high.

I'd like to upgrade to vB3 and add a lot of new features. So I am thinking that I need a dedicated server with something close to these specs:
- P4 2GHz
- 1GB RAM


I've checked out Rackshack (ev1servers.net), prices are great ($150/mo for what I need) but they have no uptime guarantee.
I am with OLM.net right now, it would be about $250/month for the specs I need. Thier support is good, but I am worried because of the problems I am having (server basically shuts down once I use up my RAM).

I've looked at some others but I was wondering if anyone has specific experience with a host and running a site as large as mine.