If we exceed 384-MB, we would have to purcha$e more memory .. at a rate of $7.50/month per additional 64-MB RAM.
Here's what I found » the highest amount of RAM we've used thus far is 366-MB (see here), which equals 95% of our allowable limit. Kinda close, but this was only a short-term transient (1 hour).
Our highest *sustained* memory use is ~325-MB (lasting a few days), so that number might be more meaningful (85% max). Our average memory use tends to be in the range of 270-to-290 MB (75%)...
.. which is actually pretty comfortable. And it's not uncommon, following a reboot, for our usage to drop down to the 220-240 area, tho these low numbers tend to creep up over time (as Apache caches more pages).