I have a SW99 - its pretty much the same gun - it just comes down to aethetics. I had my SW99 first, because I couldn't get my hands on a fullsize Walther. I also hard chromed the slide.
When I had a $1200 TRP 1911 from Springfield, it was irritating because I always shot better with the SW99. So, it is a good gun.
Be aware that the SW99 is no longer made - as you pointed out, only the SW990L is. Its basically their version of the Walther QA trigger. So, the trigger is a bit heavier, but shorter than the P99 A/S style trigger of the SW99.
I have thought about the 45 version before. But, the frame and grip is bigger. And, the style of gun has a somewhat high bore axis. I don't think I'd like the gun in anything higher than a 9mm. That's why I never bought the 45 version. But, the people who have it seem to like it a lot