If you don't have the manual, here it is:
http://www.mesaboogie.com/manuals/Dual Cal DC-3.pdf
The DC-3 outputs 35 watts RMS. If you crank both the channel masters and the output up to 7 or 8, you are inching close to 70 watts peak. If you do this often, you are probably straining the 50 watt speaker a bit.
Personally, I like a speaker rated at twice the amp's wattage. In your case, that would be a 70 watt speaker. You can try plugging the 8 ohm speaker into a four ohm jack. That will lower the output power a bit.
Keep in mind, a higher-rated speaker will get you cleaner cleans, but also cleaner dirt as well. (And whiter whites! :lol: ).
I ran a Celestion Vintage 30 (60 watts) in a Maverick (35 watts) with no ill effects.
I currently have an Eminence Texas Heat (150 watts) in a 75 watt Mark III. It's working well, and the Texas Heat is supposed to break up early, so it's not as stiff as an EVM 12L.
Don't get me wrong, I love the EV. If you want a big, fat sound with more bottom end, try one. It adds 10 lbs. to the weight, 'tho.
Hope this helps