That gun in a Lobo holster is my daily carry, with 38 Spl 158g +Ps. I predict you'll like it.
Mine wears a Crimson Trace LG-305 laser grip, which makes it comfortable enough that it's my most-shot snubbie. Once I get the front sight elevation figured out at about 30 yards (I don't get to the range often enough to remember from session to session) I can usually take down the 8" steel plates 5 out of 5. (My red laser isn't visible that far in daylight, so the plates are shot with the iron sights.)
One thing I particularly like about shooting 38s in the magnum-frame Js is that the longer barrel brings a longer ejector rod throw, which almost fully extracts the 38 case. It's quite rare when all cases don't fully extract, something I can't say about the shorter barreled J frames (of which I have several.)
While I will eventually get a 640, for now, I have (2) 642's. They are the guns that I carry, when I can't carry a gun and the difference in weight when pocket carrying, etc., at least to me is huge. If you can make the 640 work, I say go for it and good for you, but as for me the 642 is the perfect BUG or gun to wear, when I can't wear one.
J frames shoot just fine, I shot 94.7% in a 50 round shoot at my concealed carry class, that was with the small wood grips that use to come on older J frames.
Here is a link with a TON of solid information. I apologize for the fact that this is a knowledge "fire hose" just sip until you get to the section about Back Up Guns. Lots of good insight about loads and .38/357 questions.