Most people and maybe Boogie people more than most tend to stay with OEM speakers. There are many great speakers that are well worth experimenting with. I have spent a lot of time over the years trying many speakers, including most of the JBL, Electro Voice and Celestion offerings. I have also had Jensens and Webers. Changing speakers is IMO one of the easiest, least expensive and effective ways of customizing your tone. Here are a few great speakers that you might consider that I have used with MKI, II and III amps; JBL D & K series, EV FORCE, Altec 417-8H. Be careful with JBL D-120's though because they can only handle about 60 watts (They were OEM for very early Boogies and some MKI's though). Keeping in mind wattage match ups with different speaker/amp combinations and knowing it is possible to use speakers with lower ratings if you can keep the loudness level down, here are some other great speakers to try; Jensen C12N, Weber Blue Dog Ceramic, Celestion G12-65 (my favorite speaker). I still have some EVM's but currently, in my MKIIC+ Simul Class. I have an EV FORCE and I intend to try it out with the Rola Celestion G12-65 that I had in a MKIII red stripe Simul Class. I am not taking anything away from EVM's. I think they are a very good choice, especially if you have to play very loudly. Stage volumes for typical gigs is coming down and are much easier to make sound good through good PA systems when set right so you might find you can use lower volume settings and try many of the new speaker offerings to get sounds you might prefer.
I like to swap tubes too but I find that changing speakers generally makes a lot more difference.