In my experience pushing C-41 does not usually work very well, but you should be able to get ~1/2 stop without any difficulty and the film latitude will likely carry you through the other half-stop. You will probably notice the mistake most in shadows that will be lacking detail. Highlights will be somewhat lower on the characteristic curve and mid-tones will probably be ok as well. All you can really do is process the film and see how it comes out. If the pictures are really valuable then expose frames from another roll the same way and with normal settings and process it as a test. The Macbeth chart is a good target for such testing. I have not had cross-over problems when pushing C-41 by 50%, so you should be ok on color balance. I think you might want to process a test roll at 4 min. or even 4-1/2 minutes figuring that processing less time will be somewhere in between normal and a maximum push. Post some results and let us know how things work out.