Thinking about Flash

(This entry is duplicated at the DPReview Olympus SLR forum) Although I've been photographing for many years, I've never been a flash user. I've only ever used flash on point&shoots for family-type photos. During the last few years I've been getting more interested in wildlife photography, and can appreciate the benefits of fill-in flash. Thus I'd like to buy my E-1 a 1-year birthday present. I'm not sure if to buy the FL36 or FL50, and apart from the power I'm not sure I understand the difference between the two. Given that I'm unlikely to get into anything like portrait photography or anything where the flash is the principal light source, and that my main interest is going to be fill-in, can anybody tell me which I'd be best served with ? I'm a bit wary of buying the FL36 and then feeling I sold myself short in 6 months, but then again I don't want to buy the FL50 and find it is total overkill.