Hi Bellycrawler,
I would keep your MMC Ultra's.
IMO, they are one of the best carbine hunting tools.
This Bowketted one does 60 consistent shots at 11.4 ft/lbs using 15.89 gr JSB's.
It has a slightly longer cylinder than standard, and a self regulating valve setup.
I think a JB tune is worth every penny.
This means you could continue to enjoy your Ultra's.
Hope this helps.
Cheers, Louis