Make sure you're keeping on top of your reciprocal rule.
Example: at the 500mm end of that lens, you'll want to consider the original 500, + the 1.5x crop, so you'll have an effective focal length of 750mm.
Shutter speed should be higher than that. Think 1/800 or faster. 1/1000 or 1/1250 would be better. Unfortunately, that lens also has a fairly slow aperture at the long end, so with the older camera, you may well not have good performance at the ISO levels required to get the shutter speed that high. Especially once you stop it down a stop or two to get your max performance
That said, if you're on a solid tripod you can reduce the shutter speed a bit and use multiple shots to increase your keeper rate.