This spec is an average of 100hz to 3khz and the 8351B actually has 400W (250+150) and two drivers covering that range unlike the single one on the 8050B.
For bass, the "long term max SPL" spec is the one to look at. The IEC weighted noise is pink noise which is downsloping, so it's primarily testing the woofer, and it's 103dB for the 8351B vs 101dB for the 8050. Not that much difference.
However, the 8351B uses the same midrange/tweeter as the 8361A and it plays a LOT louder, 8-10dB. Depending on how bass heavy your music is, or if you're using a sub, there are cases where the 8351B will play a lot louder. It just depends.
I mean we've talked about this in a zillion threads before. The differences are:
- Coaxial
- Incrementally smoother dispersion and flatter FR with no crossover dip/narrowing.
- 3-way design, reduces overall distortion(imd), but unknown audibility
- GLM/etc (you can get this from the 8350A too ofc)
"how much and is it worth it" is a personal choice, that's all it can ever be. Some people like me absolutely can't stand vertical changes in FR so the only bullet point that matters is the first one. Some people care most about price/performance, and have their own room correction/EQ, therefore the 83xx monitors don't make sense for them.
If price/performance is very important to you, which it sounds like it is, I would stick to the 8000-series and its close competitors.