Hey Shadowhawk,
I have a
WSM 22.5 and the temps are off by 40 degrees compared to my ET-733. The location of the probe on the
WSM also has an impact as it probes at a higher level then a probe which will sit close to your meat.
As for charcoal, I have used both Briquettes and Lump Charcoal (hardwood), and in my opinion both have pros and cons...
You may find that Briquettes tend to burn a little longer, maintain temperature better, and can be slightly cheaper, however they can take a little longer to light (not a huge issue), some may produce a slight chemical smell, and they do produce more ash then Lump Charcoal)
In regards to Lump charcoal; lights quickly, some say you can burn hotter (however not what we are looking for in low n slow cooking), quicker temp adjustment time, little ash to clean afterward, and all natural. On the down side you may have a harder time getting your temp steady, might be a little more expensive, and my pet peeve, some of the pieces are small and tend to fall out of the chimney making a small mess).
To be honest, I always used briquettes until Walmart had some of the lump charcoal on special...so been using that for my last few smokes. But overall not a big difference....that said if I was going to do a long smoke like a butt or brisket...I might go out and grab a few bags of briquettes (Typically use the Kingsford brand).
One thing you don't want to do is get those match light (instant light) briquettes...my brother picked those up without realizing when attempting his first smoke...man I the temp rose up to over 600F in less then 3 minutes! LOL
Cheers!