If you get a nice high from 30 mg hydrocodone, I might warn you not to accept 40 mg as the new 'desired dose' because you enjoyed 40 mg more than 30 mg, which would very likely be the case. Treat it as a 'treat experience', something to be kept special. You will, probably, notice the difference to a significant degree in the strength of the opiate experience, but I do not think you could be in the face of much danger IF you can handle 30 mg without issue. There may, however, be some side-effects that could be more prominent, if you experience any on 30 mg, or possibly new ones if you don't experience side-effects at your 30 mg dose. In all of the above, I am talking about hydrocodone alone. You want to make sure you are not consuming too much APAP, very toxic to the liver, as it does exist in the most common hydrocodone preparations available. APAP's harm can be sneaky, for you don't always feel the toxic effects until it is too late - I advise using a CWE method, if you don't already, and if you are taking a decent amount of APAP (2 grams [2,000 mg] and over for a single dose is getting a bit unsafe). I don't know how much APAP there is within the particular preparation of hydrocodone, but sometimes there is quite a bit per pill. Really, do be careful about this - it is a very real, very present danger that takes more than just a few lives. Again, look into a CWE (Cold Water Extraction) - there are guides on how to do them easily here on BL and all over the internet.
One more thing on the hydrocodone; if nauseated, for you might be with a bit higher dose, lie down, or at the very least sit down - people often underestimate the control of opiate-nausea with simple techniques such as those.