Deja Vu. Feel like I've replied to a query like this more than once already. But I'll be happy to repeat myself once more again...
I'm using Visual Sound Route 66 to push my Mark V.
Why?
Oh, the MkV sounds great on its own, no doubt. There's absolutely no need to boost it with anything!
...But I'm always greedy for even more sonic options, and the Visual Sound offers them in spades - in one compact, relatively inexpensive package that combines a 808 clone OD section and a compressor section. Either can be turned on or off separately. On its own, the OD section is a faithful TS-808 replica - but it's also got an extra bass boost switch if you find the traditional 808 tone too high mid-heavy. The compressor can be used simply as a compressor and a clean boost but it also has a tone control that can be switched on or off.
I've become addicted to how this simple pedal expands my sonic options. I like to roll back the preamp gain on the Mark V and then engage the Route 66 as a clean boost for extra gain when I need it. Or dial in a JCM 800 style crunch sound on channel 2, then engage the OD section for instant 1980s heavy rock/metal sounds. Or engage the compressor section + channel 3 for some really liquid legato shredding. And so on. It's amazing how many more different sounds you can get out of your Mark V with just one extra pedal.
The downside: it's built in China. While it doesn't suck your tone like cheap pedals tend to do, the compressor section is a bit noisy: if you crank the "COMP" pot, it will produce an audible hiss (but that's no big deal since in a live situation, it will get lost in the band mix anyway).