I prefer a minimum OVT of 500, when planning to register a domain. However, it does not hurt if it is lower when all you want is just to create a page for it.
There are still many keywords with high OVT, just be wiling to do your research including on other extensions and other languages (also considering the specific OVT server for that specific language).
Just last week I registered about a hundred with OVT minimum of 10,000. But I spent lots of time on them.
In my view, OVT shows about 10 times more searches than Wordtracker, but it varies a lot. The best would be Trellian since it uses several search engines together, not just Yahoo used by OVT. However, WT shows you the correct sequence of words, what OVT does not. This is very important.
To compare Wordtracker and OVT side by side try:
http://www.digitalpoint.com/tools/suggestion/
Trellian:
http://www.keyworddiscovery.com/search.html
Google Trends and MSN AdCenter are good as well, but limited.
...
Regarding possible hits, you have to consider not only the "High OVT" but also the number of competing web sites (number of search results in Google/Yahoo) because they will be "sharing" that high OVT with yours. In this case, SEO is the answer.
HTH.