You will see a huge difference! I started out with PCs, them went to T5HOs and thought that was a huge difference (corals grew bigger/faster, colors were more vibrant). Now with metal halides, everything looks evenz better, even the colors on my fish look better. I highly recommend upgrading if you have the opportunity.
Just make sure you know hold old the HQI bulb is. They're only good for about 1 year. I bought mine used with 10 month old 10K bulbs and used them to acclimate everything to MHs and then swapped to knew 14K bulbs.
Good luck!