Selecting the right output transformer

[guitarboy58]

I've been contemplating building the power amp section of a 5E5 Fender Pro (the cathode biased version) in my next build except I'd like to use KT66 tubes and drop the output to about 30W.   I'd like to have the tubes on the edge of break up when the amp volume is at a reasonable stage level (loud enough to be heard over acoustic drums).  My 18W and 22W builds are plenty loud but are a little too distorted at this volume.  My hope is going from 6V6 to KT66 and boosting the wattage slightly will get that extra headroom. 
With that in mind, is there any tonal/behaviour difference in running with B+ around 400V, using a higher primary resistance (say 6.6k or 5k) on the output transformer verses using the 4k recommended anode to anode resistance and lowering B+ to get the desired wattage?  I'm guessing the 4k/lower B+ will distort earlier, but I have no experience doing this. 
And the follow-up question would be, is the KT66 misapplied/under-utilized in this application?  Any thoughts or experiences would be greatly appreciated.
Thanks for your help.