Hmmmm...... one of the key words I picked up on in your post was "invest". Probably one of the best investment lights on this forum would be any of the new releases from McGizmo (he has his own sub-forum).
He has been releasing a new "wave" of titanium lights about once every month or so lately, and they are generally considered to be some of the finest custom lights available. However....... they usually sell out in a few hours...... a day at most, so you kind of have to keep checking his forum to make sure you catch the "wave".
Be prepared to pay between $400-500, but also realize that if you are lucky enough to get one, you won't have any trouble selling it later (if you are crazy enough to do that), as there are always more folks who want them than there are lights available.
Don's lights are special..... every collection should have at least one. Some of the older models can occasionally be found in the B/S/T forum.
Or.... you could check out some of the custom lights by Milky.... the multiple LED versions with a flupic or other multiple level driver control. I'm strongly considering getting one of his SF L1 mods... where he lets you pick the kind of beam you want for it.... I prefer more of a floody beam.... but there is nothing like working with a modder to get a light just the way YOU want it.
Anyway, it looks like you are on your way. Have fun!