Some people have converted 5E3s to fixed bias instead of cathode bias - this is not ideal if you don't want to hurt tone, as it will change. Putting 6L6s in is self defeating without other extensive changes - the output transformer for 2 6V6s in pushpull has double the impedance 2 6L6s require, and the amount of power even from a s-s rectifier is nor really greatly increased, because cathode biasing tends to dissipate a lot of extra power as as heat. 6L6s to me change the tone and loose a lot of the sweetness of the Deluxe.
The three things you can do if you haven't already:
1. Use a 12AY7 in the front slot. The amp is designed for it in terms of component values in the preamp, and it actually increases headroom without sacrificing volume and maybe takes the amp up another notch before breakup, depending on guitar.
2. There is a mod called the Paul C mod which will increase headroom slightly
I have done this to both the 5E3s I built and I rate it a solid improvement in general. It also increases volume and takes breakup a little higher on the dial.
3. Get the most efficient speaker - a Celestion Blue is exxy but will provide a solid volume boost compared to most others due to it's fantastically high efficiency.