I've used them with 8 watt SET amps with great success, though I think the low end drivers ultimately do require a bit more power.
In my system when pairing Super Eclipse III's with Coincident Frankenstein 300b amps, I have not found that to be the case. I have not found the combination lacking or rolling off.
In other direct comparisons I have found the Coincident Frankensteins to be on par with some 845 based SETs in terms of their ability to drive, so they may outperform their rating.
If you prefer tubes they should definitely be on your short list. ;)