Anybody else ever done this...

In the past year+ that I have been on FT, one of the valuable lessons I learned (the hard way BTW), is to try to select routing that allows me to be on the largest aircraft possible. The pecking order seems to be,

1. Widebodies
2. 752
3. 320
4. 319
5. CRJ700

On 752's I usually like seat 4D or 5D (and have NEVER missed an upgrade on this metal either). With all the "metal changes" I have been reading about lately, I have started choosing seats 2C or 3C thinking that if the metal is downgraded or changed, I'll still have a seat in F. My question is am I being paranoid or simply being cautious???