If you always wanted it, and you have the money, buy it! If you are thinking in terms of investment, it all depends if this artist’s market is on the way up, or down, or nowhere. Often an artist’s best (most famous) works are never available on the market, and that market may be on the up and up, then, 40% could be a good deal. Typically the top works sell at a premium to everything else, so, for example, if the market doubles, the best work can go up three times, comfortably. I hope this helps- and so my advice is: Go forth unafraid!