Well keep in mind I'm on a 19-row cooler as well. I've seen up to 260 in the later summer so far (at this track), and 250 driving a bit harder/longer in November (same track again). Unfortunately this weekend's forecast is mid-70's even though we're just about in the center of winter, so I expect 250-ish again. I figure 5W40 might do me a little more good than 5W30 at that sort of range. Probably a hair too thick down in the 180-220 sort of range I see DD-ing in the winter, but then again I'm not pushing the engine all that hard DD-ing either, so it's not so critical
Either way the difference between 5W30 and 5W40 isn't likely to be tremendous.