Those are good classical choices. I have the predecessor to the dp2070sb-bk, the dp2060u. I couldn't be happier with it. It has excellent overall focus and geometry and purity and is in line with all the excellent reviews that I've read. Ghosting is absolutely traceless. The only downfall is the high degree of vertical moire in high rez patterns. The dp2070sb-bk is the new flagship and has a m2 superbright tube. Based on the reputation of previous models, this one should be good too, though it is somewhat early to tell (it was just released). Macworld named it the best of some show covention (i forget). Mitsubishi's dp series are highly recommend from a variety of different sources (pcworld, displaymate, thg). They are the only non-apple monitors sold in the apple store(if it really means more than a marketing deal of some sort).
I've not seen a g520, but I've owned a cpd-e540 (a step lower with lower resolution capabilities) which was promptly returned for major ghosting and color impurities. I also noticed very bad geometry. Not a small gripe was it's poor text sharpness at it's native resolution of 1600x1200. My personal experience from sony hasn't been good in that regard. However, subjectively, the sony did appear brighter and contrasty and more vivid overall as well as just everso slightly flatter.
If displaymate award means anything, the dp2060u won the best AG crt alonside the f520 which is sony's $1600 flagship with all the bells and whistles. The interesting thing is that the mitsu's retail price is half the f520.
Unless I could see a g520 first hand, I'd personally go with the mitsubishi. If I would dare spend the money, I'd try out the gdm f520.
generally, pricewatch.com and pricegrabber.com are great sites for just about anything. you'll soon learn this if you hang out on the web.
you could probably find the dp2070sb-bk for ~$760 us dollars. the g520 ( the g520p means you'll pay more for the case design) is also ~$670.
you might want to check out neoseeker.com for reviews as well as pcworld.com and thg and displaymate.com (not review but awards).
Quality is better than name brand, even regarding beloved AMD.