I love Rotella T6 5w40 Synthetic in other cars. Sent oil samples out for analysis and the rotella is great stuff.
Not sure about it in the Esprit. Lotus specs a 50 or 60 wt oil. Makes me think the Lotus built these engines with some loose tolerances. a 40wt oil may not be thick enough to keep bearings from getting wiped out.....probably not going to happen, but just a thought.
The oils with higher ZDDP (like the Deisel truck oils) can hurt the catalytic converter. Usually not a problem if you have a healthy engine that isn't blowing back oil into the combustion chamber.... But the Esprit with the turbo, which generally pressurizes the crank, and the poor crank case breather oil separator, which puts oil into the intake... Every Esprit I have seen has some oil in the intake...
I would stick with the recommended 20W-50 or 15W-50 oils.
Rotella is good stuff. I've used it in the Buells before when I could not get Amsoil to top it off on trips. Diesel engine oils are the recommended replacement per Harley if Harley oil isn't available. As mentioned, it does have high levels of ZDDP, though IIRC, Mobil 1 V-Twin actually contains more.