The Kurt Kinetic curve is (in my experience measuring with a PowerTap and confirmed by things I've read) pretty optimistic from an absolute numbers perspective, but a 10% gain in 4 weeks from a minimal fitness base seems reasonable. You won't see that kind of gain consistently as your fitness closes in on your personal limits.

By optimistic, I mean 30W high at the lower ends of normal FTP ranges to 50W at the high end.

I've been working the denominator of the P/W ratio much more aggressively than the numerator this off season doing the TR Mid-Level base building program. I'm half way through stage III. I only gained 3W (a 2% increase) between my last two FTP assessments (12/31/13 and 1/27/14) but my weight dropped by 10 pounds in the same time.