I'd go with a smaller pic, but then you wouldn't be happy. Maybe you can place more than one watermark.
I tend to place 3 on mine. [link]. I have the very hidden one on the top left. You can see the M of my past username. The 2nd on the middle of the drawing, and the third on the lower right. In case art thieves remove one, they might not see the others.
You know there are other ways to deal with art theft aside from obnoxious watermarking and image resizing. In the grand scheme of things, people are going to steal your art no matter what you do. Some of them are good at editing out watermarks too, regardless of their obnoxiousness. Others don't even care that the watermark is there in the first place, they only want the image for what it shows.
What you should instead be doing is addressing the place where they are hosting the image. Generally most servers will assist you in having your intellectual property taken down. It just takes a little bit of effort.
Consider writing/designing the watermark yourself (e.g. handwritten signature/logo/stamp) so that they can't just use the same font and probably do some blending tricks, possibly removing the watermark... then again I have no idea if that sort of trick exists or not lol
Didnt read through the comments to see if anyone said this or not. but I like the fact that you incorporate your name within the art itself. That's how i knew my FB friend was using your photo. I got skeptic and took the photo into google images and your deviant art popped up.
go with the smaller resolution. The more "professional" thieves, those who will sell your prints/posters etc on ebay, can remove watermarks easily enough. Your artwork can still be appreciated in smallview.
The huge watermark on large file only deters amateurs who want to post them up in their own gallery, but prettymuch ruins it in your own gallery as well.