I would use the h.264 (having made the same transition 6 months ago), but beware it is still a codec not very suitable for editing (try scrub backwards and you know instantly what I mean). If you grade within premiere, you might want to do it in a uncompressed sequence; but then you could also go for 32bpc and have to deal with really, really huge files. Your color corrections aren’t applied to the source clip and by exporting you are of course free to choose a codec which is better for editing.
Bottom line: using h.264 you get a speed penalty – decoding a frame at a given time needs more CPU cycles – but that’s it, essentially.